22 posts · 8,897 views
Science is a lot like sex. Sometimes something useful comes of it, but that's not the reason we're doing it. --Richard Feynman- Welcome to the weblog of Björn Brembs, the owner of brembs.net. I'm a biologist with a wide variety of other scientific and non-scientific interests.
Björn Brembs
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- August 19, 2010
- 12:00 PM
- 56 views
After 40 years of research, there may be a reason why Aplysia can learn
by Björn Brembs in bjoern.brembs.blog
I'm currently in sunny southern California for some experiments at UCSD. This is the place where one can find the marine snail Aplysia in its natural habitat. As I've been working with Aplysia for about ten years now, I felt it was about time to see Aplysia in the wild and observe what these animals do when they're not in a tank waiting to be experimented upon. Just this morning, before heading out to UCSD, I went snorkeling in La Jolla Cove in the hope of seeing some specimens. All these years working on Aplysia and I had never seen one in the wild. What do they do? Why can they learn? Do they only learn about how to handle their food? I always imagined these snails as sort of the cows of the sea, living happily on their food and, being hermaphrodites, not really having any trouble finding mates, either. Any other forms of learning are probably purely coincidental of neurons in general being plastic. Unfortunately, I didn't find any Aplysia at all today. scuba.png However, when I checked the table of contents of the latest issue of the Journal of Neuroscience later in the evening, I found this great paper that was so long overdue: "Lobster Attack Induces Sensitization in the Sea Hare, Aplysia californica".... Read more »
Watkins, A., Goldstein, D., Lee, L., Pepino, C., Tillett, S., Ross, F., Wilder, E., Zachary, V., & Wright, W. (2010) Lobster Attack Induces Sensitization in the Sea Hare, Aplysia californica. Journal of Neuroscience, 30(33), 11028-11031. DOI: 10.1523/JNEUROSCI.1317-10.2010
- August 3, 2010
- 03:22 PM
- 58 views
ICN2010: One of the genetic roots of language points to self-learning in fruit flies
by Björn Brembs in bjoern.brembs.blog
In 2001, an article was published in the journal Nature that a mutation in the forkhead-domain gene FOXP2 is involved in a hereditary speech and language disorder in a family in Great Britain. Today, many refer to FOXP2 colloquially as a 'language' gene and accumulating evidence suggests that FOXP2 is involved in language-like behavior in other animals, most prominently in song-learning in birds. Language as well as song learning in birds is an operant learning process, i.e., the birds and us humans are trying out different sounds. At first, they sound nothing like speech or song, but by comparing the consequences of the 'babbling' - the sounds produced - with the desired outcome, step by step, the sounds are modified and slowly become speech or song.... Read more »
Santos, M., Athanasiadis, A., Leitao, A., DuPasquier, L., & Sucena, E. (2010) Alternative splicing and gene duplication in the evolution of the FoxP gene sub-family. Molecular Biology and Evolution. DOI: 10.1093/molbev/msq182
Fisher, S., & Scharff, C. (2009) FOXP2 as a molecular window into speech and language. Trends in Genetics, 25(4), 166-177. DOI: 10.1016/j.tig.2009.03.002
- July 23, 2010
- 10:53 AM
- 152 views
The will and its freedom: biological evidence from invertebrates
by Björn Brembs in bjoern.brembs.blog
A few weeks ago, Lars Chittka invited me to write an article "about free will in insects" for a Proceedings of the Royal Society B (Biological Sciences) Special Feature on 'Information processing in miniature brains' that he is editing. Given our work on spontaneity in flies and my mentor being Martin Heisenberg, how could I decline?I think I will first give a very brief overview of what people used to call "free will" and why it was such a controversy. I hope to get the gist across in about two paragraphs. Much of this info will be distilled from Bob Doyle's website and his article in William James Studies. Bob also published a letter to Nature in response to Martin Heisenberg's article there. Is it just coincidence that it was Heisenberg's father Werner Heisenberg who discovered the uncertainty principle?Then I plan to go on to argue that today the old, metaphysical free will of course does not exist in the almost 'spiritual' sense and that no prominent scholar has entertained that idea at least since Popper and Eccles' book "The self and its brain" in 1977. Instead, I will try and make the case that the term "free will" should be recast in biological terms, as a trait that evolved and keeps evolving to different degrees in different animals. I plan to use evidence from flies, leeches and other invertebrate animals to emphasize that even so-called 'simple' brains possess the capacity to behave unpredictably, i.e., freely. Any difference in freedom between animals is merely gradual.I probably should also spend a paragraph or so elaborating on the selection pressures leading to spontaneous behaviors and behavioral variability.Once the capacity for freedom has been shown, it will take less work convincing the readers of the capacity to 'will'.All of this should be couched in the notion that the dichotomy between indeterminism and determinism is a false dichotomy, because brains operate in the gray area between the two. This may be the most difficult concept to grasp, that indeterminism and determinism are not mutually exclusive, but delineate a spectrum of what one may call 'probabilism'. I may try and refer to evolution as also using both concepts of mutation (indeterminate) and selection (determinate) in a probabilistic process. I may even try and refer to Bayesian Statistics, although I know little more than the basic idea behind it. The main task of this section will be to argue that what we call freedom is more than just chance. Chance, or randomness is a prerequisite for freedom, a necessary component but it's not sufficient. Let me quote from our press release at the time: [co-author George Sugihara]"This nonlinear signature eliminates the two alternative explanations of spontaneous turning behavior in flies that would run counter to free will, namely complete randomness and pure determinism. These represent opposite and extreme endpoints in discussions of brain functioning which mirror the free will debate." To that, I'd only add that our subjective notion of 'Free Will' is essentially an oxymoron: we would not consider it 'will' if it were completely random and we would not consider it 'free' if it were entirely determined. Nobody would attribute any responsibility to our action if it had happened entirely coincidental. On the other hand, if our action was completely determined by external factors such that there was no alternative, again the person would not be held responsible. So if there is anything remotely close to free will, it must exist somewhere between chance and necessity - which is exactly where fly behavior comes to lie. George again finds the right words: "Our results address the middle ground between simple determinism and randomness that is currently not well understood or characterized. We speculate that if free will exists, it is in this middle ground." This leads me to believe that the question of whether or not we have free will appears to be posed the wrong way. Instead, if we ask 'where between chance and necessity are we located?' one finds that this is precisely where humans and animals differ. Humans may not have free will in the philosophical sense, but even flies have a number of behavioral options they need to decide between. Humans are less determined than flies and possess even more options. With this small reformulation, the topic of free will becomes the new biological research area of studying spontaneous behavior and can thus be discerned from the philosophical question.If after all that there's still room in the article, I'll review some of the data on the human default mode network and what they might contribute to the debate.Let's see, if enough people express interest in the comments, I may put a draft version online for comments and review. All commenters will at least be mentioned in the acknowledgements, of course.Heisenberg, M. (2009). Is free will an illusion? Nature, 459 (7244), 164-165 DOI: 10.1038/459164aDoyle, R. (2009). Free will: it's a normal biological property, not a gift or a mystery Nature, 459 (7250), 1052-1052 DOI: 10.1038/4591052cBriggman, K. (2005). Optical Imaging of Neuronal Populations During Decision-Making Science, 307 (5711), 896-901 DOI: 10.1126/science.1103736... Read more »
Heisenberg, M. (2009) Is free will an illusion?. Nature, 459(7244), 164-165. DOI: 10.1038/459164a
Doyle, R. (2009) Free will: it's a normal biological property, not a gift or a mystery. Nature, 459(7250), 1052-1052. DOI: 10.1038/4591052c
Briggman, K. (2005) Optical Imaging of Neuronal Populations During Decision-Making. Science, 307(5711), 896-901. DOI: 10.1126/science.1103736
Maye, A., Hsieh, C., Sugihara, G., & Brembs, B. (2007) Order in Spontaneous Behavior. PLoS ONE, 2(5). DOI: 10.1371/journal.pone.0000443
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- April 26, 2010
- 03:35 AM
- 210 views
In which potatoes in France are like high-ranking journals in science
by Björn Brembs in bjoern.brembs.blog
There are about 1.5 million scholarly articles published in all the sciences, spread over about 24,000 journals. Even if there were a single database or entry-point providing access to all the literature, nobody would be able to keep up with everything that is being published in their field of work any more. Desperately looking for some clue as to which publications to select for in-depth reading and which to ignore, scientists began to rank the journals according to how often the articles in these journals were cited. This ranking got started around the 1960s, when the number of journals started to proliferate. Fast-forward to today: What began as a last-ditch effort to handle an overwhelming flood of scientific information is now a full blown business. Journal ranking by citations is now done commercially by a multi-billion Dollar media corporation, Thomson Reuters. The journal rankings are sold to research institutions on a subscription basis ranging anywhere between approx. 30,000-300,000€ (US$40,000-400,000) annually.With increased visibility for the high-ranking journals came an increase in submitted contributions. The higher ranking the journal, the more readers and contributors, so the more income for the publisher. And so the vicious cycle of scientific publishing evolved: more and more scientists want to publish in and read the high-ranking journals. Due to the high volume of submissions, the publishers of these journals are in a position to pick about 2-5% of the submitted articles for publication and reject the rest, increasing the prestige of these journals even more. Sometimes these rejections are accompanied by a recommendation to submit the work to one of the lower-rank journals of the same publisher. Clearly, something has to be exceptionally 'good' to make it into a high-ranking journal (or, as some claim, have the potential to increase the journal's rank). After a few cycles, it became difficult to distinguish if a scientific finding was so 'good' that it made it into the high-ranking journals or if it had to be good because it was published there. Indeed, for some aspects of scientific life such as promotions, hiring, grant proposals or other sorts of evaluations, this question wasn't even asked anymore. Publication quality became synonymous with journal rank. Today, where a scientist has published is often more important than what was published. In all human life, scarcity and branding are two powerful factors for determining value, as I'm sure any economist can tell a story or two about. Scientists are human beings and journal rank is but one example of just how prevalent the human factor is in the scientific enterprise. Today, the future of a professional scientist is all too often dominated more by the economics of scarcity and branding, rather than science.What does all that have to do with potatoes in France?After a discussion about potatoes over lunch the other day, I stumbled across this beautiful tale, published in 1956 in the American Potato Journal on how the potato arrived in France in the 18th century: This endorsement of the potato and that of the various potato dishes served at the King's table were enhanced by placing a uniformed guard on Parmentier's potato plot. Parmentier's considerate removal of the guard at night during the harvest season is reported to have furthered the success of the potato with the King's subjects. This story so reminded me of scientific publishing. Wikipedia puts the story a little more bluntly: Parmentier therefore began a series of publicity stunts for which he remains notable today, hosting dinners at which potato dishes featured prominently and guests included luminaries such as Benjamin Franklin and Antoine Lavoisier, giving bouquets of potato blossoms to the King and Queen, and surrounding his potato patch at Sablons with armed guards to suggest valuable goods — then instructed them to accept any and all bribes from civilians and withdrawing them at night so the greedy crowd could "steal" the potatoes. Now I wouldn't know anything about bribes, but the part about creating artificial scarcity and a brand name to increase value for an ordinary object rang familiar.In a recent 'Opinion' article in one of the journals at the very top of the rank, Nature, the author correctly points out that this system of journal rank has many flaws and should be replaced by a more scientific system for the metric evaluation of science. She specifically calls for social social scientists and economists to be involved in developing this new system, underscoring the points above. Indeed, it is remarkable that our current journal rank system is still in place. After all, not only does the author and many scientists agree, but also the originators of the journal rank system, the high-ranking journals themselves and even some evaluators all have long realized that using journal rank to evaluate individual researchers is both "unfair and unscholarly". I have lamented this absurd state of affairs plenty of times right here and elsewhere. However, artificial scarcity and brand name have, by now, developed such a powerful dynamic, fueled by billions in taxpayer money and a rich history of great scientific traditions, that it seems unstoppable, even if all participating parties agree that putting an end to it would be better for science.It is with these powerful dynamics (and some analogous evolutionary dynamics) in mind that I posted an off-hand comment to the 'Opinion' article mentioned above. The comment stated that any, even the most complex and scientifically tested system will eventually succumb to social dynamics adapting the scientific community to the system and maximizing the individual participant's benefit while minimizing their costs. The only system that would be immune to such dynamics is one where the rules change more quickly than the social dynamics can follow:Wouldn't it be nice if metrics weren't needed? However, despite all the justified objections to bibliometrics, unless we do something drastic to reduce research output to an amount manageable in the traditional way, we will not have any other choice than to use them.However, as the commenters before already mentioned, no matter how complex and sophisticated, any system is liable to gaming. Therefore, even in an ideal world where we had the most comprehensive and advanced system for reputation building and automated assessment of the huge scientific enterprise in all its diversity, wouldn't the evolutionary dynamics engaged by the selection pressures within such systems demand that we keep randomly shuffling the weights and rules of these future metrics faster than the population can adapt?This comment will soon be published as a 'Correspondence' piece in the printed version of Nature. I'll update the post with the direct link as soon as it is online. Coincidentally, the current LaborJournal contains a letter from me, which states pretty much the same thing, with some additional information.Hougas, R. (1956). Foreign potatoes, their introduction and importance American Potato Journal, 33 (6), 190-198 DOI: 10.1007/BF02879217Lane, J. (2010). Let's make science metrics more scientific Nature, 464 (7288), 488-489 DOI: 10.1038/464488a... Read more »
Hougas, R. (1956) Foreign potatoes, their introduction and importance. American Potato Journal, 33(6), 190-198. DOI: 10.1007/BF02879217
Lane, J. (2010) Let's make science metrics more scientific. Nature, 464(7288), 488-489. DOI: 10.1038/464488a
- April 15, 2010
- 07:46 AM
- 164 views
Our own little Open Science project: Buridan's paradigm
by Björn Brembs in bjoern.brembs.blog
On FriendFeed, Open Science is a frequent discussion topic and I also get the impression that the scientific community at large is starting to pay more and more attention to the principles of Open Science, possibly in the wake of the Open Access movement.As a proponent of Open Science, I've always had a bad conscience that my own contribution to the movement was so ridiculously small: I just tell everybody about my results here on my blog. Most of my data is acquired in a proprietary format (hand-written Turbo Pascal programs on an 386 PC from the early 1990s!) so making them available to everybody in a readable format would require some major effort.Because I've been thinking about a way to make my research more open, we have initiated our new project with Open Science in mind from the very beginning (even though the scale is still more than modest, to be honest). A special behavioral experiment for the fruitfly Drosophila has been on my to-do list for quite some time now. I'm talking about Buridan's paradigm, an experiment in which we can test mutant or transgenic flies for defects in various parameters of sensory and motor capacities, mainly with regard to vision and walking. Buridan's Paradigm was first developed by Karl Götz in the Max-Planck Institute for Biological Cybernetics in the 1970s (see reference below). Now we finally have our own version of the experiment running! We want to make it as easy as possible for anybody else interested in such experiments, to build an apparatus themselves in order to run these tests either for research or for teaching purposes. Here's a short description of what Buridan's Paradigm is all about:To facilitate implementation by other colleagues, the software not only to track the flies, but also to evaluate the data is completely Open Source and available via the project's SourceForge website. We used the Open Source statistical package R to generate the evaluation algorithms, so anyone can go and correct bugs or develop any of the code the way they see fit. Currently, we're in the process of building a database of raw data for male and female wildtype flies to serve as reference for other users in the community. The data are in simple text format, so anybody can read an analyze this data, even if they don't want to use our software for it. We will also try and digitize the blueprints for the physical arena at some point, so we can make them accessible to the community as well. If someone knows how to do that and in which format, please contact me!With this information, anyone in the Drosophila community should be able to build such a machine and start testing flies themselves very quickly.The latest high profile publication using an advanced variant of the paradigm was published in Nature and entitled: "Analysis of a spatial orientation memory in Drosophila" (News and Views).Karl Götz (1980). Visual guidance in Drosophila Basic Life Sci, 16, 391-407Neuser, K., Triphan, T., Mronz, M., Poeck, B., & Strauss, R. (2008). Analysis of a spatial orientation memory in Drosophila Nature, 453 (7199), 1244-1247 DOI: 10.1038/nature07003... Read more »
Karl Götz. (1980) Visual guidance in Drosophila. Basic Life Sci, 391-407. info:/
Neuser, K., Triphan, T., Mronz, M., Poeck, B., & Strauss, R. (2008) Analysis of a spatial orientation memory in Drosophila. Nature, 453(7199), 1244-1247. DOI: 10.1038/nature07003
- April 14, 2010
- 05:07 AM
- 188 views
Jewel Wasps manipulate specific brain centers to turn their prey into zombies
by Björn Brembs in bjoern.brembs.blog
Jewel Wasps (Ampulex compressa) are amazing creatures and their form of parental care has received quite some attention not onkly by scientists but also from the general media, and rightfully so. This parasitoid wasp serves for its young by hunting cockroaches as food. But it doesn't serve the cockroach to the offspring in pieces. No, it first performs brain surgery on the 'roaches to render them docile and then lays an egg onto the pacified animal from which a larva will hatch which then burrows into the cockroach to eat it from the inside, without any countermeasures of the cockroach. If you don't believe me, believe the History channel:What does the wasp do to the cockroach brain to so pervasively change the way it works? Last week, Ram Gal and Frederic Libersat came a step closer to answering this question. They report in the journal PLoS One that The animal searches for specific brain regions with its stinger to inject its mind-altering venom. Insect brains have a hole in the middle, where the first part of its gut, the esophagous pases through. The part of the brain that is above the esophagous is called the supraesophageal ganglion and the part below is called the subesophageal ganglion. The researchers already knew that one target for venom injection was the supraesophageal ganglion from a previous study. For the new study, one of their experiments was to have wasps sting cockroaches in which the experimenters had removed the subesophageal ganglion. They found that the duration of the sting was extended to over three minutes, where usually it only lasts for less than 40 seconds. Maybe the wasp kept searching for the missing ganglion before it gave up?To further test if indeed the subesophageal ganglion may be the target of venom injection, the researchers injected both Procaine, a local anestetic and wasp veonom which they had milked from the animals, into the cockroach subesophageal ganglion. The result was the same for cockroaches injected with venom or with Procaine: both substances, when injected into the subesophageal ganglion, rendered the 'roaches docile, greatly reducing their spontaneous and elicited walking distances. Moreover, the researchers recorded that neural activity in the subesophageal ganglion was greatly reduced in stung and procain injected animals, compared to controls. Interestingly, injecting the substances into the supraesophageal ganglion did not have any dramatic effects, raising the question of why the animal stings there as well. The authors discuss this as follows: The exact role of the SupEG in the venom-induced manipulation of the cockroach motor behavior remains, as yet, rather elusive. Several possibilities can be offered, such as a role in evoking the excessive grooming behavior seen in stung cockroaches [13], or importance for venom-induced changes in cockroach metabolism [11]. It is also possible that the SupEG, in concert with the SEG, plays a role in inducing certain aspects of venom-induced hypokinesia either directly, by affecting specific circuitries in this ganglion, or indirectly, by affecting ascending SEG interneurons which, in turn, modulate SupEG circuitries that control motor behavior. A direct effect of the venom on the SupEG apparently contradicts previous studies which showed that decerebrated insects (i.e., those without a SupEG) tend to walk uninhibitedly (see, for instance, [23], [24], [38]–[41]), suggesting a generally inhibitory effect of this ganglion on locomotion. However, it has also been shown that certain structures within the SupEG, and especially the Central Body Complex, affect some finer aspects of locomotion, including the frequency, duration and coordination of walking, turning behavior and obstacle climbing [19], [22], [23], [35], [42]–[46]. The venom could thus, in principle, specifically manipulate these SupEG structures, in addition to manipulating SEG activity, to further control the initiation of locomotory behavior in the cockroach prey.Apart from the fascinating biology, this paper is interesting also from a more concpetual point of view. The authors do not shy away from using terms one may find controversial such as 'drive' and 'free will', e.g. in the first paragraph of their discussion: Cockroaches stung by the parasitoid Jewel Wasp (A. compressa), although not paralyzed, loose the ability to self-initiate locomotion for several days [18]. This deficit cannot be attributed to an overall sleep-like state for three main reasons. First, the deficit is highly specific, in that the threshold for initiation of other motor behaviors (such as righting, swimming, flight, etc.) is little affected [10]. Second, stung cockroaches do not assume a typical ‘quiescent’ position [28] and occasionally move their antennae in an exploratory manner. Third, when startled by a supra-threshold stimulus, stung cockroaches respond by jumping in place but do not perform the stereotypic subsequent run [14]. Thus, and since the sensory and motor systems per se are fully functional in stung cockroaches [12], [14], the wasp venom appears to specifically decrease the cockroach's drive for walking. The fact that the wasp injects its neurotoxic venom directly into the cockroach's cerebral ganglia to ‘hijack the cockroach's free will’ allows us to explore the neuronal substrate responsible for this unique behavioral manipulation.They also cite our study on spontaneous flight behavior and use the term 'rest state' which is something we are actively studying in our own experiments, ever since I read about Marcus Raichle's work on the default mode network in humans. Clearly, general brain organization is centered around the spontaneous activity of brains and how it is modulated by sensory stimuli. More and more researchers are realizing this fundamental aspect now. This, for a neurobiological study highly unusual model system provides yet one more piece of evidence that there is a pervasive and radical paradigm shift in the neurosciences in that the conceptual framework is moving away from brains as passive stimulus-response systems towards a view of brains as active organs which probe the environment by spontaneous actions and then evaluate its responses via sensory systems (brains as output/input devices). ... Read more »
Gal, R., & Libersat, F. (2010) A Wasp Manipulates Neuronal Activity in the Sub-Esophageal Ganglion to Decrease the Drive for Walking in Its Cockroach Prey. PLoS ONE, 5(4). DOI: 10.1371/journal.pone.0010019
- March 15, 2010
- 06:30 AM
- 241 views
Should scientists be in control?
by Björn Brembs in bjoern.brembs.blog
The cliché scientist is often portrayed as the laborious worker slogging away days and nights in the lab. In contrast, the cliché for musicians or artists often comprises a bohemian lifestyle, full of parties, drugs and the occasional spurts of genius and frantic artistic expression. Reality, as always, is somewhere in-between. Artists need to work hard and laboriously to get something finished before the concert, recording or exhibition and scientists need to be creative and invest a lot of thought and effort into devising the new hypothesis or the clincher experiment. In his highly readable autobiography "Physics and Beyond" Werner Heisenberg of uncertainty-principle fame tells us that, when stuck with a complicated problem, he would have to leave the institute and spend time in nature, away from everything, waiting for the creative idea to solve the problem. In today's publish-or-perish scientific culture, such behavior is a young scientist's doom. Heisenberg received his Nobel Prize at the age of 31, an age where today's scientists barely get around towards their first or second postdoc and a tenured faculty position is still about a decade away, on average.It's been known for a very long time that creativity requires a so-called 'relaxed field', meaning an absence of outside stressor distracting from the thought processes at hand. I've written before about neurobiological research uncovering the biological basis for this requirement. Today I listened to a podcast from Radio National on the "Powerful Biology of Stress", which reminded me of that post. In the podcast, Bruce McEwen, one of the researchers the host, Natasha Mitchell, interviewed, mentioned research of one of his graduate students, Connor Liston. Connor Liston had conducted a series of experiments in rats which showed that when the animal, the rat, is challenged with a complex task in which it has to shift the meaning of cues that predict where a food reward is, if the task is difficult, having either a lesion of the prefrontal cortex which other people did, or chronic stress, reduces mental flexibility. Their ability to shift is not totally gone, it's just much slower and less efficient. Confirming much previous work, chronic stress reduces mental flexibility in rats and lesion studies pointed towards the prefrontal cortex. Connor Liston found that in the prefrontal cortex, under chronic stress these neurons are shrinking, the dendrites are shrinking and they're losing connections. So they are losing a very important input—it's a reversible process, if you stop the stress it will grow back. Chronic stress leads to dendritic pruning in the medial prefrontal cortex, which probably accounts for the loss in flexibility. So far, this research is interesting, but still on the level of the rat model system. How would this research translate into humans under chronic stress? Just over one year ago, Connor Liston published a study in PNAS about chronic stress in medical students who were preparing for their board exams. he used something called the perceived stress scale, which actually asks you questions about how much in control of your life you are in and what things are causing you to be stressed out. What he also did was to develop a human task which was very much like what he did with the rats, and they used functional brain imaging to define a circuit that was activated by this task. They could observe this circuit in these stressed students and they found that the more stressed out, the less efficient was the circuit, and they also showed an impairment on this behavioural task. While dendritic pruning cannot easily be studied in live human beings, it is tempting to speculate that also in humans this process takes place in our prefrontal cortex under chronic stress and causes you to fail in behavioral tests which require mental flexibility.This kind of research shows that not only were the old reports which connected creativity with what people at the time called 'a relaxed field' correct, we are now finding out what the neurobiological basis of this connection is. This research also demonstrates even more clearly how detrimental a stressful environment is for scientists: lacking the mental flexibility to think out of the box, to distance yourself from the problem at hand to maybe find the ingenious solution, stress postpones the progress of science. Forcing scientists into habits and grunt work, stress pushes science into dead ends and wasteful spending. Today, scientists finish their PhDs when they're just about to turn 30 and receive their first own grant in their 40s. During this decade, they live on short-term contracts and any failure to publish could mean the end of a life in science. For many 40-somethings, having been scientists for all their lives, never seen a company from the inside, a dry spell at any time in their career may mean the end to any middle-class life, with salaries being so low that no large savings would ever accrue. I'm not aware of any study investigating the reversibility of dendritic pruning after a decade of existential stress, but I'm willing to hazard a guess that a scientist's most formative years are not being used to their full potential by our current system and may even be detrimental for the final decades of a scientist's work. It is also conceivable that such existential stress incentivizes fraud and other misconduct in scientists who under normal circumstances would never be prone to such behavior.Interesting for my own research is the aspect that the critical factor deciding what is considered stress in these neurobiological studies, was whether or not the rats or humans had any control over their circumstances (restraint in rats and the exams in humans). My own research focuses on how the brain learns to control its circumstances and how it detects whether it is in control or not. Maybe one day my own research will contribute to a better understanding of how to contstruct a professional work-environment that fosters science, instead of stifling it.Liston, C., McEwen, B., & Casey, B. (2009). Psychosocial stress reversibly disrupts prefrontal processing and attentional control Proceedings of the National Academy of Sciences, 106 (3), 912-917 DOI: 10.1073/pnas.0807041106Radley, J. et al. (2005). Repeated Stress Induces Dendritic Spine Loss in the Rat Medial Prefrontal Cortex Cerebral Cortex, 16 (3), 313-320 DOI: 10.1093/cercor/bhi104... Read more »
Liston, C., McEwen, B., & Casey, B. (2009) Psychosocial stress reversibly disrupts prefrontal processing and attentional control. Proceedings of the National Academy of Sciences, 106(3), 912-917. DOI: 10.1073/pnas.0807041106
Radley, J. (2005) Repeated Stress Induces Dendritic Spine Loss in the Rat Medial Prefrontal Cortex. Cerebral Cortex, 16(3), 313-320. DOI: 10.1093/cercor/bhi104
- February 17, 2010
- 03:52 AM
- 263 views
When relics are not what they have been proclaimed to be
by Björn Brembs in bjoern.brembs.blog
It is still unusual when the Catholic church allows a scientific study of one of their relics. So I was surprised to find the manuscript describing the study of the DNA of the remains of one of Europe's patron saints, St. Birgitta (Bridget of Sweden) in my PLoS One inbox one fine day in May, 2008. I'm a neurogeneticist by training, so I felt competent to take this manuscript on as academic editor. The manuscript stated that they had found through both DNA analysis and carbon dating that not only were the remains of St. Birgitta most likely not from the relevant time period, but that the remains stored with her, once thought to be her daughter, could not possibly have been from any of her relatives, let alone her daughter.Such claims, sure to stir some public attention, needed a thorough peer-review process. I selected a team of four high-caliber international experts in both the field of ancient DNA analysis and radiometric dating. I also used a scheduled visit to Uppsala, where the work had been done, to meet the last and corresponding author of the manuscript, Marie Allen, and have a good look at the laboratories where the experiments had been made. Marie was the most gracious host and took a lot of time out of her busy schedule to show me around her lab and explain how professionally she had handled the relics according to the latest techniques.The review-process was a lot more bumpy and time-consuming. The reviewers all liked the way she had handled and analyzed the DNA and only had minor suggestions for improvement in this respect. The radiocarbon dating itself was also ok, but two of the reviewers brought up the "reservoir effect". This could lead to a deviation in radiocarbon dating from the correct age if the two people had been on a high-seafood diet. To measure this reservoir effect, additional Nitrogen-dating techniques had to be applied. These proved difficult and time consuming, but after more than one year, the results were finally coming in. Indeed, there had been a measurable reservoir effect for both tested skulls, albeit not to a degree that would change the main conclusions of the study. Yesterday, almost 2 years after the initial manuscript had been submitted, the paper was finally published and I think both DNA and dating measurements are as accurate as they can possibly be, given today's technology. These measurements show that it is highly unlikely that the two skulls kept as relics by the Catholic church are the ones from St. Birgitta and her daughter. Most likely, not even one of the skulls comes from the person claimed by the church.Nilsson, M., Possnert, G., Edlund, H., Budowle, B., Kjellström, A., & Allen, M. (2010). Analysis of the Putative Remains of a European Patron Saint–St. Birgitta PLoS ONE, 5 (2) DOI: 10.1371/journal.pone.0008986... Read more »
Nilsson, M., Possnert, G., Edlund, H., Budowle, B., Kjellström, A., & Allen, M. (2010) Analysis of the Putative Remains of a European Patron Saint–St. Birgitta. PLoS ONE, 5(2). DOI: 10.1371/journal.pone.0008986
- February 16, 2010
- 02:20 PM
- 227 views
Dammit, Jim, I'm a neurobiologist, not a climatologist!
by Björn Brembs in bjoern.brembs.blog
Clouds, the sun, volcanoes, the earth's orbit around the sun, ill-defined 'natural cycles' - all have been brought up recently by a range of non-scientists arguing against the current scientific consensus that anthropogenic greenhouse gases are responsible for the global warming observed in the last century. I'm a neurobiologist, so my knowledge about climatology is rather limited, which means I don't really understand too much of the complex mechanisms underlying climate variabilities. However, I find it conspicuous that these arguments are being publicized as if nobody had thought of them before. I find it hard to believe that a bunch of amateurs should come up with serious stumbling blocks for a mature science such as climatology. But, one never knows. So I went to one of the most easily accessible archives of scientific communication, the journal Nature, and searched for "global warming". I sorted the list of publications from oldest to newest and hand-picked according to my own, subjective judgment what seemed like interesting titles and went through the most easy to follow parts of the papers. The list shows an ongoing debate among climatologists going back as far as the 1950s. As far as I could tell, all the usual suspects have been covered decades before any blogger has brought them up. Well, decades before the internet. Given that now, after basically a whole generation of debate, most climatologists are coming to a consensus (a rare event among scientists!), any amateur who thinks they can come up with something that hasn't been thought of before, should have a good and thorough read of the literature covering the last 60 odd years. This short list (and the references therin) should provide some good starters:1950s:The ice ages and past variations of the earth's climateTwentieth century man against antarctica1960s:The new look of climatology1970s:CO2 versus aerosolsMan-made carbon dioxide and the "greenhouse" effectWither climate now?Atmospheric carbon dioxide levels as indicated by the stable isotope record in woodGlacial advance relative to volcanic activity since 1500 ADFluctuations in climateAerosol and climate: hotter or cooler?Causes of climatic changeCause and effect of global coolingVolcanic triggering of glaciationOcean temperatures and large scale atmospheric variationsMan's influence not yet felt by climateNew data on climatic trendsWest Antarctic ice sheet and CO2 greenhouse effect: a threat of disasterVolcanic dust and changes in Northern Hemisphere temperaturesClimatololgy supplement 1978, e.g.:Predicting temperature trend in the Northern Hemisphere to the year 2000Solar-terrestrial influences on weather and climateClouds and the long-term stability of the Earth's atmosphere and climateImpact of CO2 on cooling of snow and water surfacesAn empirical determination of the heating of the Earth by the carbon dioxide greenhouse effect1980-1985:Scenario for a warm, high-CO2 worldCoupled effects of atmospheric N2O and O3 on the Earth's climateAlbedo change by man: test of climatic effectsGlobal warming?Detecting CO2-induced cliamtic changeSurface temperature sensitivity to increased atmospheric CO2Ice core sample measurements give atmospheric CO2 content during the past 40,000 yrIncreasing atmospheric carbon dioxide and its consequencesChanges in the solar constant and climatic effectsGlobal production of methane by termitesEl Nino Southern Oscillation phenomenonMarine biological controls on atmospheric CO2 and climateTwo views on whether more means doomVolcanic, CO2, and solar forcing of Northern and Southern Hemisphere surface air temperaturesModelling the global climate response to orbital forcing and atmospheric carbon dioxide changesDoes the ocean-atmosphere system have more than one stable mode of operation?Analytical solution for the effect of increasing CO2 on global mean temperatureA 150,000-year climatic record from Antarctic iceFuture global warming from atmospheric trace gasesI stopped collecting after this last review from January 1986, because the number of papers was just getting way too large. This is not my field of expertise, but it seems to me that all the arguments which are currently being brought up are known in the climatology community for at least 30 years, some of them have been debated for as far back as 60 years. Given such a thorough debate for such a long period of time, I trust that the current consensus of my climatologist colleagues is the best possible we can currently do. That doesn't mean it won't change, it most certainly will, that is the hallmark of science. However, given this track record, it seems unlikely that such new development will come from some blogger on the internet. Indeed, as always, there is a lively debate among climatologists, it's just not about such basics any more. Heck, I'm sure, in the next 30-60 years, some blogger will come with an argument currently being hotly debated among climatologists. ... Read more »
SAWYER, J. (1972) Man-made Carbon Dioxide and the “Greenhouse” Effect. Nature, 239(5366), 23-26. DOI: 10.1038/239023a0
- February 9, 2010
- 05:20 AM
- 307 views
Evolutionary origins of religion: weak relation to morality
by Björn Brembs in bjoern.brembs.blog
It is a long-standing argument among religious believers that religiosity were necessary for morality. In a recent Trends in Cognitive Sciences article (requires subscription), Pyysiäinen and Hauser argue that morality can arise and indeed can be found without and before any religious education and thus religion is a by-product of pre-existing cognitive properties of the brain. Indeed, religion is not ubiquitous, as for instance the Hadza's religion has been described as 'minimal', and yet, cooperation and morality are - as in all human cultures - thriving. In fact, there is a clear negative correlation between socioeconomic status and supernatural beliefs, further arguing that religiosity is not really all that important for morality to evolve or to persist. Pyysiäinen and Hauser cite a series of studies in moral psychology showing that moral judgments for unfamiliar moral dilemmas are unaffected in individuals without any religious background. In their press release, the authors conclude: "This supports the theory that religion did not originally emerge as a biological adaptation for cooperation, but evolved as a separate by-product of pre-existing cognitive functions that evolved from non-religious functions," says Dr. Pyysiäinen. "However, although it appears as if cooperation is made possible by mental mechanisms that are not specific to religion, religion can play a role in facilitating and stabilizing cooperation between groups."Perhaps this may help to explain the complex association between morality and religion. "It seems that in many cultures religious concepts and beliefs have become the standard way of conceptualizing moral intuitions. Although, as we discuss in our paper, this link is not a necessary one, many people have become so accustomed to using it, that criticism targeted at religion is experienced as a fundamental threat to our moral existence," concludes Dr. Hauser.This leaves open some other, less social cognitive factors contributing to the origin of religiosity, to which to authors allude towards the middle of their article: "[...] the concept of God is based on extending to non-embodied agents the standard capacity of attributing beliefs and desires to embodied agents. According to this view, religious beliefs are a by-product of evolved cognitive mechanisms." The authors are referring to 'theory of mind'. Besides this, still social capacity, there are several other factors contributing to the origins of religion. One such factor is of course our concept of causality and our hunt for last causes. However, the factor that is, of course, closest to my own field of research is that religion works as an operant behavior. This means that religion, for instance, can provide us with a feeling of control where, ultimately, there is none (think rain dance). This is not counter-intuitive and so I'm not the only person who has realized that this may be an important contributing cognitive factor. There is even prior evidence that when experiencing or remembering an experience of lack of control, these cognitive capacities for imagining control and order are enhanced.These insights leave us with a set of pre-existing cognitive abilities providing a fertile ground on which the evolution of religion could occur as a by-product: Our capacity to detect agency (so helpful in our social interactions that we see it even in non-living objects), together with the concept of causality imply that everything happens for a reason and that this reason is the intention of someone. This someone can be controlled using certain rituals as evidenced, for instance, by the rain occurring after a rain-dance. This someone obviously punishes you if you do not perform these rituals, so of course this someone will also punish you if you do not cooperate or otherwise violate the rules of the in-group. In this way, religion provides you with a sense of order and controllability in an uncontrollable world which, in turn, keeps you sane, your society functioning and thus competitive and alive. As one of the commenters on the press release noted, 'competitive' may be the key word here, with religion providing a further tool for promoting self-sacrifice and suicidal fighting which might have provided some particularly religious groups with a competitive advantage.Methinks it's about time for someone to develop a computer model for the evolution of religion, the data are starting to provide enough parameters for such a project.Also in reply to one of the comments on the authors' press release, a very pertinent video via Pharyngula:Ilkka Pyysiäinen, & Marc Hauser (2010). The origins of religion: evolved adaptation or by-product? Trends in Cognitive Sciences : 10.1016/j.tics.2009.12.007... Read more »
Ilkka Pyysiäinen, & Marc Hauser. (2010) The origins of religion: evolved adaptation or by-product?. Trends in Cognitive Sciences. info:/10.1016/j.tics.2009.12.007
- January 25, 2010
- 08:32 AM
- 353 views
How we discovered that an attention drug successfully treats a fruit fly memory mutant
by Björn Brembs in bjoern.brembs.blog
Blogging about one's own research always feels good: the amount of your work has accumulated enough to at least provide sufficient material for a story and some figures. It has passed the first hurdle of scientific scrutiny, peer review. On the other hand, now an exciting time begins: what will the colleagues say? Will people find the one major flaw that neither you, your co-authors, the people who proof-read the drafts before submission nor the reviewers caught? Will the results lead to new, exciting collaborations, will it be cited or will it just be met with utter apathy and complete indifference? After all, with about 1.5 million scholarly publications in approx. 24.000 journals, it's not at all unlikely that your paper just simply never is found by anyone who might be interested in it.All this of course applies to our latest paper as well. However, for those who do read it, I'm sure it will be a fascinating read. It is, without exaggeration, the craziest scientific story I've ever been involved in, an example of serendipity in science if ever there was one. Here's how it all happened. Shortly after we published our mathematical analysis of spontaneous turning behavior in stationary flying Drosophila, Bruno van Swinderen contacted me about a collaboration. I knew Bruno from before (see here and here), but we had never worked together on a project. So I was very excited to hear that he wanted me to test some of his flies in the Drosophila flight simulator, using the exact same techniques we just had published. The initial idea was to use these mathematical analyses to test his mutant flies for any abnormalities in their spontaneous behavior. However, it turned out that the mutant flies that he had sent me, radish, didn't really fly all that well, at least not well enough to generate enough data to run our mathematics on them. Neither did Bruno tell me about his results, we wanted that I should be blind as to the deficits he had found in radish. I knew radish was a memory mutant for olfactory conditioning, but that it could learn visual patterns just fine. Beyond that, nobody knew what other behavioral phenotypes this strain would exhibit.So I went on to test a whole bunch of other things for which I had the experimental setups readily available. Of all these experiments, I picked the simplest one and sent Bruno the raw data back. I just measured the flies' spontaneous turning attempts without any visual stimulation for as long as I could get the flies to fly continuously, which was six minutes. As a control experiment, the flies' behavior was measured in a flight simulator-like situation, where they could control their flight direction with respect to four visual landmarks (but still tethered, of course). I sent Bruno the data in blind, which means he didn't know which group was the wildtype control and which was the mutant group. He immediately wrote back accurately identifying the mutant group. I had no idea how he could have figured out which group was which so quickly and the experiments were basically concluded, so he started to show me his data. Bruno does something very few people on this planet are doing: he can put tiny little electrodes in the flies' brains and record their brain waves. Now with this particular mutant strain, he found that they had a peak in the power spectrum of their brain waves at around 1.6 Hz. Stunningly, when he computed the power spectrum of their turning behavior (i.e., my data), he also found a peak at about 1.6 Hz, but only when the flies were flying with the four visual landmarks. The peak was much less pronounced when there were no explicit stimuli in their environment. It was by this peak that he had recognized the mutants so quickly. But what could this peak mean? One thing it could mean is that the mutant flies become fidgety, if there's something in the environment they need to pay attention to. About one and a half times per second, the flies are initiating some turning maneuver, which can be seen as a peak in the power spectrum. In other words, the flies are hyperactive or fidgety, in this very well-defined, oscillatory kind of way. He then went on to tell me that they also were more easily distractable than the wildtype controls, both in behavior and by inferring from their brain waves when presenting them with various competing visual stimuli.I thought this was really quite amazing. Flies which are known for their memory loss are both hyperactive and have an attention deficit. I immediately thought of people with attention deficit / hyperactivity disorder (ADHD). They also have learning problems. As a joke, I suggested we put the flies on Ritalin, the drug used to treat patients with ADHD. Bruno replied that these data were actually intended for a different publication, but they indeed would fit very well with this one, too. I was flabbergasted! He had already done the experiments with methylphenidate (Ritalin is just the trade name). To my utter astonishment, the flies on methylphenidate performed like their wildtype counterparts in almost all of the tests we subjected them to. This is even more amazing when you consider that the mutated gene, radish, is required during brain development (late during pupation) and not during the behavioral test. In other words, methylphenidate rescues a deficit in adulthood that even a healthy copy of the originally mutated gene cannot rescue any more. I find it absolutely crazy to find a fly model for a human psychiatric disorder. On top of that, Ritalin, the drug used to treat ADHD in humans actually also successfully treated the flies. It's even more crazy to find all that by accident, without even looking for it! All we wanted was to study some interesting fly mutants to learn more about some basic brain function. How can it be possible to find something like this just by serendipity? My favorite hypothesis is that there are some fundamental principles about how all brains work and we have stumbled across one of them. We still don't know what it is or how it works, only that it has to do with how brain allocate attention to different processing streams. It is tempting to speculate that this process has to do with switching of activity between separate networks, but there currently is no data to tell either way.I do have plenty of other interesting results from this mutant, both in flight and in walking. However, I cannot make much sense of them, yet, so a lot of further research is required before part two of this story can be presented.Of course, as usual, I have a copy of the paper, together with all the supplementary material, on the download page.van Swinderen, B., & Brembs, B. (2010). Attention-Like Deficit and Hyperactivity in a Drosophila Memory Mutant Journal of Neuroscience, 30 (3), 1003-1014 DOI: 10.1523/JNEUROSCI.4516-09.2010... Read more »
van Swinderen, B., & Brembs, B. (2010) Attention-Like Deficit and Hyperactivity in a Drosophila Memory Mutant. Journal of Neuroscience, 30(3), 1003-1014. DOI: 10.1523/JNEUROSCI.4516-09.2010
- January 7, 2010
- 11:11 AM
- 304 views
Social filtering of scientific information - a view beyond Twitter
by Björn Brembs in bjoern.brembs.blog
It's not information overload, it's filter failure (Clay Shirky)Bonetta (2009) gave an excellent introduction to the micro-blogging service Twitter and its uses and limitations for scientific communication. We believe that other social networking tools merit a similar introduction, especially those that provide more effective filtering of scientifically relevant information than Twitter. We find that FriendFeed (already mentioned in the first online comment on the article, by Jo Badge) shares all of the features of Twitter but few of its limitations and provides many additional features valuable for scientists. Bonetta quotes Jonathan Weissman, a Howard Hughes Medical Institute investigator at the University of California, San Francisco: "I could see something similar to Twitter might be useful as a way for a group of scientists to share information. To ask questions like 'Does anyone have a good antibody?' 'How much does everyone pay for oligos?' 'Does anyone have experience with this technique?'" It is precisely for such and many more purposes that scientists use FriendFeed, which allows the collection of many kinds of contributions, not just short text messages. Also in contrast to Twitter, comments to each contribution are archived in that context (and without a time limit), providing a solid base for fruitful, threaded discussions. In your user profile, you can choose to aggregate any number of individual RSS or Atom 'feeds', including scientific publications you bookmark in your online reference manager (e.g. CiteULike or Connotea), your blog entries, social bookmarks (Google Reader, del.icio.us, etc.), and Tweets; and any other items you wish to post directly to your feed. You then look for other users whose profile is relevant to your work and subscribe to them. Every individual item posted in your subscriptions will then appear on your personalized FriendFeed homepage, plus optionally a configurable subset of the feeds you subscribed to. You can choose to bookmark ('like') any of these items (Facebook copied this 'like' functionality just before it bought FriendFeed), comment on them, and share discussion threads in various ways. At first, this aggregation of information and threaded discussions might seem daunting. However, the stream of information can be channeled by organizing it into separate sub-channels ('lists'; similar to but more versatile than 'folders' in email), according to your personal preferences (e.g. one for search alerts). In addition to individual users, you can also subscribe to 'rooms' that revolve around particular topics. For example, the "The Life Scientists" room currently has 1,267 members and imports one feed. The feature that makes FriendFeed truly useful is its social filtering system. Active discussions move to the top of your FriendFeed homepage with each new addition, which automatically brings them to the attention of you and everyone else who reads those feeds. In a sense, the most current and the most popular entries compete for attention at the top, making notifications unnecessary. This means that your choice of both rooms and subscriptions affects and filters the content you see. In that way, for instance, you could set your preferences such that you would only see papers with a certain minimum number of 'likes' among your colleagues. Alternatively, you can opt to hide items with zero likes or comments, ensuring that only those that someone found interesting will reach you. Thanks to a very fine-grained search functionality, threads also remain easily retrievable. Some of the synergistic effects of the many scientists interacting on FriendFeed are already apparent at this early stage of adoption. FriendFeed provides a convenient way to microblog from conferences by means of dedicated threads or discussion rooms created for the event, thus allowing to share comments within and across sessions, or even with people not physically present at the meeting. Such conference coverage has even received direct (e.g. ISMB09, BioSysBio09) or indirect (e.g. ISMB08) support from the conference organizers. Above and beyond conference coverage, scientists use FriendFeed to share papers, experiences on laboratory equipment, resources for teaching, or anything else commonly asked at mailing lists. A number of real-world scientific collaborations have already been sparked from such interactions. Collaborative grant proposals have been initiated, submitted and some of them approved after the idea was passed around and discussed on FriendFeed. Several bioinformatics problems have been solved by code-sharing and advice. Articles in scientific journals have been published by FriendFeed users after meeting and discussing on the platform [1-5]. Of course, since FriendFeed was not designed for scientists, there is room for improvement in terms of usability for scientific purposes. For instance, files can only be uploaded upon starting a thread, not while commenting on it, and there is currently no functionality which infers a measure of reputation to a user from his/her contributions (though the wide-spread use of real names somewhat allows that to be imported). As with all online contributions, citability and long-term archiving are unresolved issues, as is the permanence of services whose source code is not public. Fortunately, the development of social networks tailored to the needs of scientists is actively being pursued from various angles. The Polymath projects, in which researchers collaborate online to solve mathematical problems, provide a number of examples. The recent award of two NIH grants of over $US10M each for exactly such purposes is another. Ultimately, the continued enthusiastic adoption of the sophisticated variants of social filtering tools by a broad community of researchers interested in sharing their science will only increase the usefulness for and thus the capabilities of the online scientific community.References: Lister, A., Charoensawan, V., De, S., James, K., Janga, S. C. C., Huppert, J., 2009. Interfacing systems biology and synthetic biology. Genome biology. 10 (6), 309+. http://genomebiology.com/2009/10/6/309Saunders N, Beltr‹o P, Jensen L, Jurczak D, Krause R, et al. (2009) Microblogging the ISMB: A New Approach to Conference Reporting. PLoS Comput Biol 5(1): e1000263. http://dx.doi.org/10.1371/journal.pcbi.1000263 Neylon C, Wu S (2009) Article-Level Metrics and the Evolution of Scientific Impact. PLoS Biol 7(11): e1000242. http://dx.doi.org/10.1371/journal.pbio.1000242Daub J, Gardner PP, Tate J, Ramskšld D, Manske M, Scott WG, Weinberg Z, Griffiths-Jones S, Bateman A. (2008): The RNA WikiProject: community annotation of RNA families. RNA. 14(12):2462-4 http://dx.doi.org/10.1261/rna.1200508 Huss & al. The Gene Wiki: community intelligence applied to human gene annotation. http://dx.doi.org/10.1093/nar/gkp760 Acknowledgment: This comment has received input from a number of FriendFeed users, as detailed in this thread, and was jointly blogged today by Björn Brembs (Friendfeed, this blog post), Allyson Lister (FriendFeed, blog post) and Daniel Mietchen (FriendFeed, blog post).... Read more »
Bonetta, L. (2009) Should You Be Tweeting?. Cell, 139(3), 452-453. DOI: 10.1016/j.cell.2009.10.017
- December 27, 2009
- 11:15 AM
- 388 views
Intrinsic plasticity: the 'other' learning mechanism
by Björn Brembs in bjoern.brembs.blog
A quote from Nobel Laureate Eric Kandel in the December 11 issue of Science reminded me of a short article by David Glanzman covering a remarkable paper on pan-neuronal (aka 'intrinsic') plasticity and its involvement in learning and memory. Here is the quote:Q: Synaptic plasticity is a central concept in your work on memory. You've been working with Aplysia since 1962. What else do you think we can learn from these lowly snails? With almost all kinds of synaptic changes, there is a parallel change in the excitability of nerve cells. For example, in Aplysia, a number of neurons fire spontaneously, in bursts. If you [stimulate] a bursting cell [synaptically], you can change its bursting activity for long periods of time [which implies plasticity not only in the synapse but the neuron itself]. This just blew me away. [But] I've never come back to it. I received this quote from my postdoc advisor John Byrne. He traced Eric Kandel's mention back to an old finding in Aplysia published in 1977. By now, of course, intrinsic plasticity is a well-documented phenomenon, but its complexity has so far hampered research into the relationship of synapse-specific plasticity and neuron-wide, intrinsic plasticity. Moreover, some forms of intrinsic plasticity appear to be somewhat input-specific, for instance, if the affect only certain branches of the neuron, containing many synapses. Now, Jack Byrne and my then fellow postdoc in his lab Riccardo Mozzachiodi have published a very timely review on our current understanding of intrinsic plasticity with regards to synaptic plasticity, entitled "More than synaptic plasticity: role of nonsynaptic plasticity in learning and memory".The review covers many examples from both vertebrate and invertebrate model systems and is a great primer into the 'other' learning mechanism. The review does of course not yet include the paper on the involvement of Na/K pumps in intrinsic plasticity as this paper came out just now, a few weeks after Mozzachiodi and Byrne was published. This new paper shows that not only ion-channels contribute to intrinsic plasticity, but even such seemingly 'boring' molecules as Na/K-ATPases.I became interested in intrinsic plasticity since evidence started to come in that operant conditioning was relying on intrinsic plasticity in Aplysia. Now that also in Drosophila it appears that a completely different set of genes is required for modifying behavioral circuits during operant conditioning (or self-learning, as we have recently defined it), while the well-known synaptic plasticity genes are not required. Maybe this differential genetic requirement reflects the mechanisms also differentially affecting synaptic vs. intrinsic plasticity? Could it be that intrinsic plasticity allows to modify the firing properties of a central neuron in a behaviorally relevant network and thereby affecting the entire network, rather than just some small-scale property in it? If this were the case, it would make a lot of sense to regulate such far-reaching network alterations and only allow them after sufficient training - which is exactly what we just found in Drosophila. Thus, there is quite some circumstantial evidence suggesting that synaptic and intrinsic plasticity may also be behaviorally differentiable. However, no clear direct experimental evidence is available, yet.Interestingly, a PubMed search for "Intrinsic plasticity" OR "intrinsic excitability" yields only 274 articles (with only a handful of papers before 2000), while a search for "synaptic plasticity" yields 8564. Anybody out there looking for a cutting-edge research field?Pulver, S., & Griffith, L. (2009). Spike integration and cellular memory in a rhythmic network from Na+/K+ pump current dynamics Nature Neuroscience, 13 (1), 53-59 DOI: 10.1038/nn.2444Pulver, S., & Griffith, L. (2009). Spike integration and cellular memory in a rhythmic network from Na+/K+ pump current dynamics Nature Neuroscience, 13 (1), 53-59 DOI: 10.1038/nn.2444... Read more »
Pulver, S., & Griffith, L. (2009) Spike integration and cellular memory in a rhythmic network from Na /K pump current dynamics. Nature Neuroscience, 13(1), 53-59. DOI: 10.1038/nn.2444
- October 18, 2009
- 02:38 PM
- 359 views
How brains generate variable behavior
by Björn Brembs in bjoern.brembs.blog
Animals constantly have to adapt to varying environmental conditions, explore new situations and figure out new strategies to catch prey or avoid predators. On the other hand, they need to be able to behave consistently in a largely deterministic environment. Brains reflect the complex mixture of chance and necessity in the environment in thier structure and function.One great example of this was just explained to me here on a poster at the annual meeting of the Society for Neuroscience (SfN). The poster was entitled "Distinct inhibitory neurons exert temporally specific control over activity of a motoneuron receiving concurrent excitation and inhibition" and came out of the lab of Klaude Weiss at Mount Sinai. The researchers work on the neurophysiological model system Aplysia. They study how the neurons in the buccal ganglia control the movement of the radula (a tongue-like organ) during feeding. Other scientists in the lab have shown previously that Aplysia feeding behavior is highly variable, probably to be able to adapt to a large variety of different food sources. What was unknown until now is how the neurons in buccal ganglia which control feeding behavior generate this variability. This is what this poster was about.They showed that the seemingly simple, two-phase behavior of the radula coming out of the jaws (protraction) in the open state, and pulling food into the mouth (retraction) in the closed state is subdivided neuronally into smaller chunks of behavior. For instance, using electrodes in multiple neurons at once, they figured out that the closure state of the radula during retraction consists of an early phase and a late phase. The motor neuron which controls the closure of the radula is identified and is called B8. By recording the activity of various identified neurons in the buccal ganglia, as well as by de- or hyperpolarizing them in a quiescent preparation or during feeding motor programs actively generated by the ganglia in the dish, Sasaki et al. teased apart how excitatory and inhibitory input converges on B8 during retraction. The excitatory input makes B8 fire and the radula closes. Two neurons provide inhibitory input for B8. Depending on how rapid they fire and when, B8 fires less strongly and the radula closes less strongly or stays open. One of these neurons, called B70, fires in the early phase of retraction and the other, B4/5, fires late during retraction. On the poster, the researchers show how the delicate balance between tonic excitation and early/late inhibition by these two neurons allows the animal to close the radula more or less, earlier or later, depending on what is the most successful strategy with whatever food the animal is currently attempting to feed on.This delicate balance is a great example of how brains keep their behavior flexible and variable: by keeping the behavior always on the edge of one or another state (open or closed in the case of the radula), it only takes the smallest variations in any neural activity and it may have large effects on the behavior. The researchers also showed that there are peptidergic modulations going on in this balance, allowing for longer-term fine-tuning of the balance. I find these results very exciting, because the provide a compelling example of a potential mechanism for how behavioral variability is generated, which we have studied in the fruit fly Drosophila. It's exactly this 'critical' state in a labile balance which may serve as one of the mechanisms which generate the sort of variability we have also observed in Drosophila.This research has just been published in the Journal of Neuroscience, so you can have a lok at all the exciting results for yourself:Sasaki, K., Brezina, V., Weiss, K., & Jing, J. (2009). Distinct Inhibitory Neurons Exert Temporally Specific Control over Activity of a Motoneuron Receiving Concurrent Excitation and Inhibition Journal of Neuroscience, 29 (38), 11732-11744 DOI: 10.1523/JNEUROSCI.3051-09.2009... Read more »
Sasaki, K., Brezina, V., Weiss, K., & Jing, J. (2009) Distinct Inhibitory Neurons Exert Temporally Specific Control over Activity of a Motoneuron Receiving Concurrent Excitation and Inhibition. Journal of Neuroscience, 29(38), 11732-11744. DOI: 10.1523/JNEUROSCI.3051-09.2009
- August 20, 2009
- 01:20 PM
- 538 views
How the brain is and isn't like a muscle
by Björn Brembs in bjoern.brembs.blog
Use it or lose it, they say. The saying holds not only for muscle fitness, but also for the brain. The Romans already knew that 'mens sana in corpore sano' and today we know that both physical and mental fitness, exercise and training can stave off many signs of aging. Even debilitating diseases such as Alzheimer's disease can be delayed, or at least their symptoms reduced by staying physically and mentally fit and active. I recently handled a manuscript in my function as Academic Editor for the journal PLoS One, which suggests that the analogy goes even further.The paper entitled "Endogenous Human Brain Dynamics Recover Slowly Following Cognitive Effort" has now been published and I thought it's worth highlighting.The authors of this study used functional magnetic resonance imaging or fMRI for short (colloquially: brain scanner). In 2001 Marcus Raichle coined the term default network for the brain areas that were discovered to be active when the test subjects in the scanner were at rest, i.e. not occupied with any task. The existence of this default network is a puzzle, as one would assume the brain would reduce its activity in the absence of any explicit tasks, given the high energetic cost of neural activity. Instead, the brain keeps running at ~99% of maximum load, even when we're not doing anything. This is precisely where the brain isn't like a muscle: muscles don't keep on contracting when we rest.But I wanted to explain how the current paper extends the analogy.Well then. Barnes et al. evaluated brain activity in a rest-task-rest experiment. This means they continuously scanned the brains of the participants before, during and after a cognitively demanding working memory task. Each participant went into the scanner twice, once with the task level set to easy and once with the level set to difficult. The way they analyzed their data is another way in which the brain is like a muscle, the heart muscle. Like heart beat and other physiological measures, the slow fMRI fluctuations also show fractal scaling behavior. We also found similar mathematics in our analysis of spontaneous fly behavior which was one of the reasons I became interested in the default network in general and in this manuscript in particular. The authors looked at one such measure, the Hurst exponent. Comparing this H-exponent before and after the difficult and easy task, respectively, Barnes et al. found that it can take several minutes until the H-values reach pre-task values after the task. Moreover, this time was extended after high cognitive load, compared to the low cognitive load task.These results make the brain even more like a muscle: after we use it, it takes some time for the brain to come back to the state in which it was before we used it. I'm not sure fatigue would be the right word to describe what is going on there, but the practical implications of this work are clear: what if you have designed an experiment where the rest periods between the tasks are shorter than the few minutes found in this study? Will the earlier tasks influence the brain scanner readings of the later tasks?But I found these results interesting for a much more general reason. The function of the default network is still a mystery. We know it's altered in patients, ranging from Alzheimer’s disease, autism, depression, schizophrenia, and attention-deficit-hyperactivity disorder to post-traumatic stress disorder, Tourette syndrome or amyotrophic lateral sclerosis. It's not surprising that it is thought to underly daydreaming and creativity. As such it may be involved in planning and strategizing. Mechanistically, the default network seems to be competing with the task related-networks in a sort of push-pull system: whenever we perform a task, the default network is suppressed and the network required for the task is enhanced. As soon as the task is over, the default network comes back online (albeit slightly disturbed from the task for some minutes as Barnes et al. show). Moreover, sometimes, the default network comes back during the task. The instances where the default network is 'pushing through' are usually the ones where the participant is making an error. Even if the participant is not making any errors, there seems to be a little default network activity left during the task and the variability in these fluctuations explain about 80% of the variability in the behavior during the task.All of this looks a lot like internal and external processing are competing for the computing capacity of the brain. Evolutionarily, this hypothesis would fit a lot of circumstantial evidence from other, basically unrelated fields. For instance, I recently blogged about a study which suggested that the ancestral organization of behavior may have been motor-sensory or output-input, meaning that stimuli only modulate ongoing activity, rather than eliciting behavior directly. This organization would also fit the solution of the explore-exploit dilemma underlying habit formation described in another recent blog-post. According to the hypothesis, the default network would underlie (at least to some extent) exploratory behavior (or at least the behavioral variability required for exploration) and repetition (or stress) would suppress the default network when habits are formed or executed. It also fits with our fly data showing that the variability in spontaneous behavior is decreased when the flies are flying towards an object as opposed to not having any visual cues.Could it be that this push-pull relationship between external and internal processing is not just a special feature of mammalian or even primate brains, but of all brains? It could explain why brains seem to passively react to external stimuli in one set of experiments (default network suppressed), but to actively explore the environment in other experiments (default network active). It would mean that brains are indeed not input-output devices, but neither are they output-input devices. Maybe they are both at the same time and neither function alone would lead to evolutionarily stable brains?To answer this question we need to look for default networks also in other brains. Unfortunately, this is technically somewhat tricky and the microscope I'd need to do that in flies costs about half a million Euros. I'm in the process of finding out how and where I have to apply to get my hands on one of these. If indeed this push-pull organization were universal, it would be the first evidence-based formulation of a general principle of brain function. It would fit a host of observations from a variety of different fields and model organisms. In what exciting times we are living! Barnes, A., Bullmore, E., & Suckling, J. (2009). Endogenous Human Brain Dynamics Recover Slowly Following Cognitive Effort PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006626... Read more »
Barnes, A., Bullmore, E., & Suckling, J. (2009) Endogenous Human Brain Dynamics Recover Slowly Following Cognitive Effort. PLoS ONE, 4(8). DOI: 10.1371/journal.pone.0006626
Maye, A., Hsieh, C., Sugihara, G., & Brembs, B. (2007) Order in Spontaneous Behavior. PLoS ONE, 2(5). DOI: 10.1371/journal.pone.0000443
- August 3, 2009
- 09:05 AM
- 517 views
Don't stress the scientists!
by Björn Brembs in bjoern.brembs.blog
“very absent-minded persons in going in their bedroom to dress for dinner have been known to take off one garment after another and finally to get into bed, merely because that was the habitual issue of the first few movements when performed at a late hour”William James, 1890It is difficult to kick a habit. Like riding a bike – once automated, some behaviors can stay with us for a lifetime. Life-long memories are a familiar trait. After all, they define who we are. We can recall important events in our lives in sometimes astounding clarity and detail. In the last 40 years, neuroscience has made great progress in understanding how the brain accomplishes this amazing feat. Sometimes after a single exposure to a salient stimulus, synapses in the brain can permanently alter their properties to encode complex, vivid memories. If synaptic plasticity is so fast, why does it take practice to learn how to ride a bike, why repetition to form a habit?The ultimate, evolutionary causes for the need to practice our skills are obvious. Skills and habits convey an enormous benefit as they free up processing power and allow us to efficiently carry out often-used behaviors with little effort. The repetition required to automate these behavior buys us time to pick the best sequence of movements to do the task. Without the need for practice, we may be stuck with whatever movements we used when we first tried to master the skill, often unsuccessfully. There must have been strong selection pressure on the neurobiological mechanisms (the proximate causes) which would allow for rehearsal time before behavioral memory was actually consolidated. One could think of any number of mechanisms which would slow down memory formation, from inefficiencies or delays in the intracellular processes altering synaptic transmission to initially weak reinforcement signals, scaling with the increasing success of the behavior. Yet, evidence from our ow experiments with the fruit fly Drosophila points to a different mechanism, namely dynamic interactions between multiple memory systems. We founsd that the memory system responsible for habit formation is temporarily blocked by the memory system dealing with learning about our environment. Interestingly, switching off a part of the fly brain called the mushroom-bodies halved the amount of practice required to form habits, suggesting that the mushroom-bodies are involved in this blockage (as they are not directly involved in memory storage, they most likely mediate the interaction coming from the environment-memory storage system).Now, almost simultaneously, two groups have published research that another treatment, stress, can lead to rapid habit formation in rats and humans as well. In almost identical experiments, the subjects were either stressed or not during operant conditioning experiments. In these experiments, the subjects had to perform two actions for two different kinds of food. After training, one of the two kinds of food was given to the subjects until they were sated. This feeding to satiation is the critical part of the experiment. Imagine you would like to eat a treat and a machine would make you work for salty or sweet treats. Obviously, when you've had as much sweets as you wanted, you'd work harder to get the salty treat than the sweet treat. What research into habit formation has shown, is that this specific reduction after devaluation no longer occurs when the training has taken place long enough to form a habit. Both animals and humans then just keep working the machine to get noth treats in equal number. Just placing the animals/people in front of the machine makes them follow their habit, similarly to the absent-minded people in former times who got undressed and went to bed, just because they were in their bedroom at a late hour. These two studies now showed that the two groups (stressed and unstressed) differed in their specific reduction after devaluation: the stressed groups behaved as if they had been trained for much longer and habitually worked the machine equally hard for both treats, even after relatively short training.One of the authors of the study is my esteemed colleague Rui Costa, who I'm currently writing a grant for organizing a conference on actions and habits with. In a recent article in The Scientist he said: It's not that they are stupid and don't understand that there is a difference. It's just that when given a choice, they will do the automatic thing. In fact, these stress-induced changes seem almost adaptive. When we are under chronic stress, it could be advantageous to use habitual strategies because [it reduces] the amount of cognitive resources that you need. Thus, Rui also emphasizes the adaptive value of habits, to reduce cognitive load and allow the brain to focus on the more pressing issues and not how to best execute a behavior. The amount of training required to form a habit is flexible and reflects the trade-off between behaving flexible and behaving efficiently. If need be, we can form habits just as fast as we can learn facts, faces or events. (see also PhysOrg)In a more colloquial formulation of the flexibility/efficiency (or exploration/exploitation) dilemma, one could say that habit is the enemy of creativity. It was German ethologist Konrad Lorenz who postulated that creativity requires a so-called "relaxed field" in which no stressors apply. Now, about three decades later, the biological experiments are being initiated to find out how the brain operates to give rise to this requirement.Creativity is also a necessary prerequisite for doing innovative science. This means that stress is the enemy of good science. In our publish-or-perish culture with it limited contracts and constant fear of joblessness and failure, I wonder how many excellent scientists fall by the wayside, because they were never able to fulfill their full potential? Does this research argue for small, managable research groups in which there is a lot of time for interaction, free-thinking and relaxed brain-storming, rather than large, high-throuput labs in which everybody is just a cog in a large machinery producing scientific data, rather than doing science? Could this sort of research help us design the environment which maximizes on the brain capital of the individual scientists? Or will it just eventually lead to a treatment which enhances the blockade of habit formation, extending it indefinitely, no matter how stressful your life is, such that you will become for ever creative?Schwabe, L., & Wolf, O. (2009). Stress Prompts Habit Behavior in Humans Journal of Neuroscience, 29 (22), 7191-7198 DOI: 10.1523/JNEUROSCI.0979-09.2009Dias-Ferreira, E., Sousa, J., Melo, I., Morgado, P., Mesquita, A., Cerqueira, J., Costa, R., & Sousa, N. (2009). Chronic Stress Causes Frontostriatal Reorganization and Affects Decision-Making Science, 325 (5940), 621-625 DOI: 10.1126/science.1171203... Read more »
Schwabe, L., & Wolf, O. (2009) Stress Prompts Habit Behavior in Humans. Journal of Neuroscience, 29(22), 7191-7198. DOI: 10.1523/JNEUROSCI.0979-09.2009
Dias-Ferreira, E., Sousa, J., Melo, I., Morgado, P., Mesquita, A., Cerqueira, J., Costa, R., & Sousa, N. (2009) Chronic Stress Causes Frontostriatal Reorganization and Affects Decision-Making. Science, 325(5940), 621-625. DOI: 10.1126/science.1171203
Brembs, B. (2009) Mushroom Bodies Regulate Habit Formation in Drosophila. Current Biology. DOI: 10.1016/j.cub.2009.06.014
- July 13, 2009
- 03:19 PM
- 538 views
The first motor-sensory system?
by Björn Brembs in bjoern.brembs.blog
On the first day of last year's Gatsby workshop on "smaller cognitive systems", Gasper Jekely told us about their remarkable work on how the larvae of a marine polychaete worm (Platynereis dumerilii) perform phototaxis. Gaspar introduced his work by saying that these larvae may be very similar to the common ancestor of all bilaterally symmetric animals (Bilaterians), the Urbilaterian. The Urbilaterian being the last common ancestor of vertebrates and invertebrates, this would mean (and I have no reason to doubt) that we can learn a lot from the original state of that animal's nervous system. All of today's extant vertebrate and invertebrate nervous systems must be some variation of this initial organization.In the Nature paper entitled "Mechanism of phototaxis in marine zooplankton" (req. subscr.), Gaspar tells us the whole story in magnificent detail, full color and almost as fascinating and exciting as in his talk last year. These larvae are planktonic, moving around in the sea using a ring of cilia, beating to propel the animals forward. In the early larval stage, they move towards the light (positive phototaxis), moving them away from the place where they hatched (dispersal). Later in their development, the become negatively phototactic. This behavior brings them back to the ocean floor, where they metamorphize into the adult worm (probably quite some ways away from the place where they first hatched).The animals look sort of like an egg with hair (I'll refrain from alluding to any resemblance to living or fictional characters):The larva also has two eyes on the bald spot above the 'hairs'.It uses the cilia ("hairs") to generate a stream of water from front to back, propelling it through the water. Apparently, in the dark the animals move about randomly.When there is a light source, the two eyes of the larva can detect the direction from which the light is coming. The right eye detects light from the right and the left eye light from the left. Each eye has a shielding pigment to the center of the animal, to prevent light from the opposite direction from exciting the photoreceptor in each eye.The photoreceptor of each eye makes a direct, inhibitory synaptic connection to the most nearby ciliated cells:This means that whenever the photoreceptor detects light, it will inhibit the ciliated cells nearby, causing the cilia to beat with a lower frequency. In the graph below, all the cells are numbered around the equator of the larva, with cells #6 and 7 being closest to the eye.As you can see, in the dark, the frequency of the cilia in beats per second is significantly higher close to the eye, compared to when light is being shone on the larva.This reduction in ciliary frequency has the same effect as if you'd stop rowing on one side when you're on a lake, rowing: you turn towards the side where you stopped rowing. In much the same way, the larvae turn towards the light, by inhibiting the ongoing activity of the propelling cilia on the side on which there is light.Gaspar and his colleagues used a wide variety of methods including evolutionary biology, physiology, microscopy, behavioral biology and computer modelling to come to a truly astoundingly detauiled conclusion as to how these animals perform directed orientation maneuvers with very few nerve cells. The level of detail, sophistication and rigor is really exceptional in this publication.Superficially, what this fantastic work of science shows is how a stimulus (light) elicits a response (phototaxis) via sensorimotor processes. However, if you look at the physiology of how the larvae are actually performing the behavior, it becomes clear that this appearance is not supported by the data presented in this paper. Platynereis larvae generate ongoing behavior even in the absence of light. If the experimenter, the rotation of the earth or their own behavior leads to activation of the eye(s) by light, this light-stimulus only modulates (in this particular case inhibits) the behavior that was already present before any stimulation. Thus, the general organization of the Urbilaterian nervous system was not characterized by sensorimotor, but by motor-sensory processes. In the beginning was the behavior, dispersing the larvae. Only later, sensory processing started to provide an evolutionary advantage by modulating the behavior and directing the animal first towards light and then away from light.These results contrast with most neuroscientific research today which works under the assumption of the sensorimotor hypothesis, stating that the main function of brains is to produce behavior in response to sensory stimulation. This new research suggests that at least the ancestral state was the reverse: brains are generating behavior and then await the response of the environment.Jékely, G., Colombelli, J., Hausen, H., Guy, K., Stelzer, E., Nédélec, F., & Arendt, D. (2008). Mechanism of phototaxis in marine zooplankton Nature, 456 (7220), 395-399 DOI: 10.1038/nature07590... Read more »
Jékely, G., Colombelli, J., Hausen, H., Guy, K., Stelzer, E., Nédélec, F., & Arendt, D. (2008) Mechanism of phototaxis in marine zooplankton. Nature, 456(7220), 395-399. DOI: 10.1038/nature07590
- May 17, 2009
- 10:21 AM
- 700 views
In which a Nature paper fails on several levels
by Björn Brembs in bjoern.brembs.blog
Ok, so what else is new? We all love to rip GlamMag paperz to shreds in our journal clubs. This paper by Hong et al. last year in Nature stands out of the crowd in two main ways. For one, it shows how failing to realize alternative explanations can easily break your entire publication. Moreover, it shows how generating large datasets doesn't replace using your brain when generating and evaluating them. Apparently, the editors and reviewers at Nature handling this particular manuscript failed to take this into account this one time.The authors went through unbelievable efforts to test an enormous number of different wild type, mutant and transgenic Drosophila strains for their temperature preference. Based on only 8 authors, it seems to me these authors must have worked 24/7 for many, many months to get all this data, evaluate them and discuss and compile all the results. Here's their experiment:Pretty self explanatory: the flies walk around in a chamber with a temperature gradient and where they spend most of their time determines their temperature preference. From this sort of data, the authors calculate a preference index for high or low temperatures, respectively:According to their graph, flies walking around incessantly score an AI of zero both for high temperatures and for low temperatures (center pane of the graph). There is a structure in the Drosophila brain that is associated with hyperactivity: the mushroom-bodies. The study was published exactly ten years before Hong et al.: Mushroom bodies suppress locomotor activity in Drosophila melanogaster. Apparently, the authors are unaware of this publication, as they don't even cite it. However, the authors of this previous paper have used a very similar setup (horizontal tubes) and tested flies for their walking activity:In this graph (Fig. 2 from Martin et al., 1998), the mutant mbm1 as well as transgenic fly strains which have synaptic activity blocked in various parts of the mushroom-bodies (line 201Y, H24 and 17D) show increased walking activity. Now let's see how these flies perform in the temperature essay from Hong et al. (Fig. 1, modified to show just selected strains):As expected, the flies show an AI of around zero (with black bars denoting AI low and grey bars AI high). But Hong at al. have not suspended critical thought entirely before they submitted the results of their intensely laborious screening efforts. They realized there was a need to control for some sort of locomotion defects in the flies they tested. However, their control also fails on several levels: a) they used a climbing essay when in their temperature essay the flies were walking horizontally and b) the climbing performance in their essay could only decline and not increase:Thus, the authors could not detect the increase in walking performance that inhibiting mushroom-body function conveys (Martin at al., 1998).In summary: Hong et al. conclude that the mushroom-bodies are involved in temperature preference by using a locomotor essay that reproduces the results of an experiment published ten years earlier (Martin et al. 1998). Somehow adding insult to injury, they tested an absolutely incredible number of fly strains (more than 120, by my count), yielding no less than 30 pages of supplementary material with many figures, tables, text and references (but again, no citation of Martin et al. 1998 in there). Yet, they only manage to show the same thing as Martin et al. in 1998 with 10% the number of strains.Important: Of course, all this does not exclude that the mushroom-bodies and the processes in the neurons there controlling cAMP level indeed may be involved in temperature sensing and temperature preference. It's only that Hong et al. haven't shown that, yet.References: Hong, S., Bang, S., Hyun, S., Kang, J., Jeong, K., Paik, D., Chung, J., & Kim, J. (2008). cAMP signalling in mushroom bodies modulates temperature preference behaviour in Drosophila Nature DOI: 10.1038/nature070901. Jean-René Martin, 2. Roman Ernst, & 3. Martin Heisenberg (1998). Mushroom Bodies Suppress Locomotor Activity in Drosophila melanogaster Learning and Memory, 5, 179-191 DOI: 10.1101/lm.5.1.179... Read more »
Hong, S., Bang, S., Hyun, S., Kang, J., Jeong, K., Paik, D., Chung, J., & Kim, J. (2008) cAMP signalling in mushroom bodies modulates temperature preference behaviour in Drosophila. Nature. DOI: 10.1038/nature07090
1. Jean-René Martin, 2. Roman Ernst, & 3. Martin Heisenberg. (1998) Mushroom Bodies Suppress Locomotor Activity in Drosophila melanogaster. Learning and Memory, 179-191. DOI: 10.1101/lm.5.1.179
- May 8, 2009
- 04:28 AM
- 600 views
Noise in the brain?
by Björn Brembs in bjoern.brembs.blog
I was recently alerted to a group of theoretical publications which deal with the issue of apparent 'noise' in neuronal populations. The Nature Reviews Neuroscience article "Neural correlations, population coding and computation" by Bruno B. Averbeck, Peter E. Latham & Alexandre Pouget covers this area quite well.Basically, the authors claim that the variability one can see when recording from the brain when the same stimulus is presented repeatedly is noise and must be detrimental for the tranmission of information and hence a problem the brain must solve:Part of the difficulty in understanding population coding is that neurons are noisy: the same pattern of activity never occurs twice, even when the same stimulus is presented. Because of this noise, population coding is necessarily probabilistic. If one is given a single noisy population response, it is impossible to know exactly what stimulus occurred. Instead, the brain must compute some estimate of the stimulus (its best guess, for example), or perhaps a probability distribution over stimuli.It needs to be noted that the authors do not refer to sensory neurons, which code sensory information with great precision. Instead, they look at neurons deep in the mammalian brain, many synapses away from the primary sensory afferents. What I don't understand from their article is why this should be considered 'noise'. Obviously, if high fidelity between the site of sensory input and the site of recording were required, there would be a single axon going there, and not via many syapses. Synapses are time consuming and energetically expensive. During development, unused synapses are being pruned throughout the brain. Thus, the variability must reflect some computation which takes place in the synapses from the site of sensory input to the site of recording. Let me illustrate this with a picture:Of course, if one records from neuron NR and stimulates sensory neuron NS, as in A, there is a lot of processing going in in the synapses along N1-4. This is happening even without any external input into the single conveyor belt of information. Of course, there never is such a conveyor belt, there are always inputs, feed-forward and feedback connection. But even in this simplest model of information transmission, every synapse is a computational component and not just a link between neurons adding variability to the sensory signal. These synapses would not be there if this processing was not some important brain function. This is illustrated in B: if simple and reliable information transmission from NS to NR were important, there would only be one single axon from NS to NR, without any additional processing.I would really like to hear good arguments as to why the recorded variability should be 'noise' and a problem for information coding, rather than a reflection of the brain doing what it's supposed to do: finding out what the best action is under the current circumstances.Averbeck, B., Latham, P., & Pouget, A. (2006). Neural correlations, population coding and computation Nature Reviews Neuroscience, 7 (5), 358-366 DOI: 10.1038/nrn1888... Read more »
Averbeck, B., Latham, P., & Pouget, A. (2006) Neural correlations, population coding and computation. Nature Reviews Neuroscience, 7(5), 358-366. DOI: 10.1038/nrn1888
- October 24, 2008
- 12:24 PM
- 901 views
No brain is too small for a memory
by Björn Brembs in bjoern.brembs.blog
I'm trying to catch up with my backlog of research news (~600 unread messages) and what do you know, the first one is already worth blogging about! Researchers from the Brooklyn College in New York have tested classical conditioning in Nautilus. This was an interesting experiment, because Nautilus (which is a cephalopod like squid, cuttlefish and octopus) doesn't have the structures known to be important for forming memories in this group of animals. So in true Pavlovian fashion, they flashed a blue light into their tanks, just before they got fed. In the memory tests, they just flashed the light and observed the animals without food. Just like Pavlov's dogs which salivate after a tone was paired with food to the tone alone, Nautilus shows anticipation of the food by extending their tentacles to the blue light alone up to a day after conditioning.Without a vertical lobe, these animals must use a different structure to store classical memories than other cephalopods. This result reinforces my opinion, that the minimum you need for a memory to form are two neurons and a synapse between them. Plasticity is probably a characteristic of all neurons. In this case, there ain't no such thing as a brain too small to learn. Citation: R. Crook, J. Basil (2008). A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea) Journal of Experimental Biology, 211 (12), 1992-1998 DOI: 10.1242/jeb.018531... Read more »
R. Crook, & J. Basil. (2008) A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea). Journal of Experimental Biology, 211(12), 1992-1998. DOI: 10.1242/jeb.018531
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