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Archive for January, 2006

This year it is 150 years ago that miners in the German Neander Valley lucked upon 16 fossils that turned out to belong to a different homo species. The Neanderthals are of special interest to the study of the homo sapiens brain, being bigger in average volume, but (presumably) different in function. Since brains doesn’t fossile there are really only two ways of studying this difference: (1) through comparing the DNA of the two species, and (2) through what has been called cognitive archeology – the deduction of how the Neanderthal mind must have been organized through an examination of archeological evidence such as diet, technology and social structure.

If you happen to read German this article in Die Zeit kicks off the Neanderthal year. In July Bonn will host a big conference on the Neanderthals. Its web-site has a number of interesting papers on-line.

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Mirror neurons

On a hot summer day 15 years ago in Parma, Italy, a monkey sat in a special laboratory chair waiting for researchers to return from lunch. Thin wires had been implanted in the region of its brain involved in planning and carrying out movements.

Every time the monkey grasped and moved an object, some cells in that brain region would fire, and a monitor would register a sound: brrrrrip, brrrrrip, brrrrrip.

A graduate student entered the lab with an ice cream cone in his hand. The monkey stared at him. Then, something amazing happened: when the student raised the cone to his lips, the monitor sounded – brrrrrip, brrrrrip, brrrrrip – even though the monkey had not moved but had simply observed the student grasping the cone and moving it to his mouth.

The researchers, led by Giacomo Rizzolatti, a neuroscientist at the University of Parma, had earlier noticed the same strange phenomenon with peanuts. The same brain cells fired when the monkey watched humans or other monkeys bring peanuts to their mouths as when the monkey itself brought a peanut to its mouth.

Later, the scientists found cells that fired when the monkey broke open a peanut or heard someone break a peanut. The same thing happened with bananas, raisins and all kinds of other objects.

“It took us several years to believe what we were seeing,” Dr. Rizzolatti said in a recent interview. The monkey brain contains a special class of cells, called mirror neurons, that fire when the animal sees or hears an action and when the animal carries out the same action on its own.

By now mirror neurons is a well-known story. However, if you are not up to speed Sandra Blakeslee has a nice story in NY Times giving a short run-down of the story so far. (The quote above is from that article.) Afterwards, you will probably enjoy a visit to the homepage of the Physiology Lab at Parma University. That’s the home of many of the pricipal investigators working on the mirror neuron cells, including Giacommo Rizzolatti, Leonardo Fogassi, and Vittorio Gallese. They have a lot of their research papers on-line.

I’m chiefly mentioning this because I’m going to put up the next installment in my little series on the neurobiology of culture in a few days. (See the first part here.) Here, mirror neurons play a vital part, and you may want to get a head start!

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Hardwired Behavior

This book from Cambridge University Press looks interesting. I haven’t actually read it yet, but the new issue of Nature has a rather positive review of it. A brief passage from the review:

Laurence Tancredi’s book Hardwired Behavior powerfully presents science that shows the gross inadequacy of the binary terms we often use to talk about the genesis and character of complex human behaviours. He writes: “Our brain structures are not immutable; they are susceptible to change for the better and change for the worse.” Indeed, much of the research he discusses rests on this neuroplasticity. He reports on research showing that talk therapy can produce neuronal changes. His chapter on gender differences suggests that changing social conceptions of the roles of women “will inevitably affect the biology of their brains over time”. He reports on research showing that rats deprived of nurture at birth fail to express a gene that is correlated with their ability to handle stress. And he refers several times to a fascinating study by Avshalom Caspi and colleagues (Science 301, 386–389; 2002), which found that the likelihood of children becoming antisocial as adults is a function of both their genomes and their experiences. As Tancredi observes, this finding “emphasizes the interactive nature of genes and environment, nature and nurture”.

Tancredei, L. (2005): Hardwired Behavior. What Neuroscience Reveals About Morality. Cambridge University Press.
Publisher’s description.

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Until recently anatomists were convinced that humans are born with all the neurons they are ever going to own. In the first years of life, some of theses neurons are then pruned due to a dynamic selection process. From then on, the only serious change to the brains was thought to come from cell death or inflicted lesions.

Not so. The brain actually continues to rebuild itself throughout life. For instance, new cells are born in the hippocampus. And a new study from a group at MIT demonstrates that adult dendrites of non-pymidal neurons are able to expand their branches. Here’s the abstract:

Despite decades of evidence for functional plasticity in the adult brain, the role of structural plasticity in its manifestation remains unclear. To examine the extent of neuronal remodeling that occurs in the brain on a day-to-day basis, we used a multiphoton-based microscopy system for chronic in vivo imaging and reconstruction of entire neurons in the superficial layers of the rodent cerebral cortex. Here we show the first unambiguous evidence (to our knowledge) of dendrite growth and remodeling in adult neurons. Over a period of months, neurons could be seen extending and retracting existing branches, and in rare cases adding new branch tips. Neurons exhibiting dynamic arbor rearrangements were GABA-positive non-pyramidal interneurons, while pyramidal cells remained stable. These results are consistent with the idea that dendritic structural remodeling is a substrate for adult plasticity and they suggest that circuit rearrangement in the adult cortex is restricted by cell type–specific rules.

The paper was published in PLoS Biology which means it is open-access. Go grap it!

Lee, WCA. et al. (2006): Dynamic remodeling of dendritic arbors in GABAergic interneurons of adult visual cortex. PLoS Biol 4(2): e29.

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The most recent issue of Nature Neuroscience contains a truly amazing study by the Thomas Insel-group. Insel and his colleagues have for many years studied pair-formation in prairie voles. Earlier, they have demonstrated that dopamine transmission within the nucleus accumbens (Nacc) facilitates partner-preference formation (i.e., that the infusion of dopamine into Nacc makes male pairie voles seek out female mates). In this new paper, they demonstrate that the rostal shell of Nacc actually contains two different dopaminergic receptors that perform functionally different jobs. One type, called D2, facilitates the approach behavior associated with the formation of a pair-bond. The other, D1, maintains that bond, by antagonizing the activity of the D2-receptors. This “faithfulness” is expressed behaviourally by the male voles figthing off other female voles than the partner. Crucially, D1-receptors are upregulated after the pair-bond has been formed. In other words: the male vole’s brain changes with having a relationship – it, figuratively speaking, becomes faithful. Thus, the behavioural process of finding a mate, establishing a relationship and keeping it going depends upon a complicated molecular process in parts of the prairie vole’s reward system. This result opens at least two exiting new avenues of ressearch: (1) Will we find the same functional system in the human brain? What is the genetic reason for a vole having more or less D1-receptors, i.e. being able to form long lasting pair-bonds?

I personally wouldn’t be surprised if Insel one day receives the Nobel prize. Being the director of NIMH shouldn’t hurt!

Aragona, B. et al. (2005): Nucleus accumbens dopamine differentially mediates the formation and maintenance of monogamous pair bonds. Nature Neuroscience 9: 133-139.

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The problem with arm-chair hypotheses such as the Sapir-Whorf idea that the language you speak determines how you think, is that they are all-or-nothing contentions. Either language determines thought, or it doesn’t. Either the mind is innate, or it is the result of nurture. Things tend not to be so clear-cut. In the next issue of Trends in Cognitive Science Paul Kay and Terry Regier review research done on colour perception – an old Whorfian theme. Turns out that colour naming and colour cognition is neither strictly universal, nor strictly language specific. Say Kay & Regier:

The ‘Whorfian’ debate over color naming and colorcognition has been framed by two questions: (1) Is color naming across languages largely a matter of arbitrary linguistic convention? (2) Do cross-language differences in color naming cause corresponding differences in color cognition? In the standard rhetoric of the debate, a ‘relativist’ argues that both answers are Yes, and a ‘universalist’ that both are No. However, several recent studies, when viewed together, undermine these traditional stances. These studies suggest instead that there are universal tendencies in color naming (i.e. No to question 1) but that naming differences across languages do cause differences in color cognition (i.e. Yes to question 2). These findings promise to move the field beyond a conceptually tired oppositional rhetoric, towards a fresher perspective that suggests several new questions.

This review nicely complements the study Thomas mentions below.

Kay, P. & Regier, T. (In press): Language, thought, and color: recent developments. Trends in Cognitive Science, to appear.

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While we’re at it with cosmetic neurology, there is also a nice article by Chatterjee freely available in Neurology. I think the conclusion in this paper says it all:

In this paper, I have raised issues about cosmetic neurology that our profession will encounter. We may have our personal opinions on the correctness of such “treatments,” but do we have a stand as a profession? We can anticipate facing questions where separating principle from prejudice is not easy and for which there are no easy answers. To make these questions concrete, I invite readers to consider their own views on the following questions:

  1. Would you take a medication with minimal sideeffects half an hour before Italian lessons if it meant that you would learn the language more quickly?
  2. Would you give your child a medication with minimal side effects half an hour before piano lessons if it meant that they learned to play more expertly?
  3. Would you pay more for flights whose pilots were taking a medication that made them react better in emergencies? How much more?
  4. Would you want residents to take medications after nights on call that would make them less likely to make mistakes in caring for patients because of sleep deprivation?
  5. Would you take a medicine that selectively dampened memories that are deeply disturbing? Slightly disturbing?

Such questions are not simply thought experiments. Patients and advocacy groups encouraged by direct advertising to consumers will raise them. How will you respond to these “patients” when they turn to you as the gatekeeper in their pursuit of happiness?

-Thomas

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In the growing field of cosmetic neurology, an approach that seeks to enhance the brain’s workings, one branch seeks to develop new drugs that not only help those suffering from memory disorders such as dementia. The question is, if it works in these patients, how would it work in healthy individuals? Several studies on both humans and other primates and mammals now show that our memories CAN be enhanced through pharmacological interventions.

So, now it can be done. Question is: should we do it? I think your answer partially depends on how you view how our brains are constructed and how they work. It seems to me that most people think that the brain (our mind) is more or less are naturally given, and highly adaptive mechanisms. To a certain extent, this is true. However, as Martin’s piece on Dehaene‘s showed, the brain is not a perfect machinery but has inherent and many flaws and shortcomings. memory is a good example. How often have you tried to remember the name of a person standing in front of you — remembering YOUR name? Or where your put your keys? Simple examples, yes. But they show that our memory is not perfect, at least not as perfect as we’d want it to be (sometimes). Just think of that 8-hours exam you read up to, just for sitting there trying to remember a piece of vital information for a key question.

So are there any memory pills out there? The piece below discusses how Targacept works on the nicotine receptor. To know a bit more on one role of this receptor system, you may also read Nancy Woolf’s article in Science & Consciousness Review.

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Targacept compounds show long-lasting improvement in cognition

Winston-Salem, NC, June 30, 2005 – In a review of research to be published in the July issue of Trends In Pharmacological Sciences, Targacept compounds were reported to have a beneficial effect on cognition well after they were no longer present in the central nervous system. For example, in preclinical animal studies, Targacept’s compounds TC-1827 and TC-1734 improved cognitive performance for up to 15 and 18 hours, respectively, though the compounds were appreciably metabolized and eliminated in less than an hour.

The authors postulate that the compounds’ long duration of effect arises from their ability to normalize levels of acetylcholine, a key neurotransmitter for modulating cognition. This mechanism of action contrasts with currently marketed drugs for conditions marked by impaired learning and/or memory, which can increase, but not normalize, neurotransmitters involved in cognitive processing.
(…)

Read more at Targacept.com

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The economic mammal

How are economic decisions made? How and why are we social? According to the traditional economic , humans are rational and self-regarding beings. Not so, says recent advances in neuroeconomics, the scientific multidisciplinary approach that studies how we make choices and act socially. On the contrary, our social interactions are thought as driven by strategic (mostly unconscious) incentives. At the least we should not think of ourselves as rational beings that are constantly choosing our own behaviour consciously. This also relates to my ongoing “dethronement” idea, especially step III.

A new article in Science by Colin Camerer and Ernts Fehr presents aspects of this discussion.

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Science 6 January 2006:
Vol. 311. no. 5757, pp. 47 – 52
DOI: 10.1126/science.1110600

Review

When Does “Economic Man” Dominate Social Behavior?

Camerer and Fehr
The canonical model in economics considers people to be rational and self-regarding. However, much evidence challenges this view, raising the question of when “Economic Man” dominates the outcome of social interactions, and when bounded rationality or other-regarding preferences dominate. Here we show that strategic incentives are the key to answering this question. A minority of self-regarding individuals can trigger a “noncooperative” aggregate outcome if their behavior generates incentives for the majority of other-regarding individuals to mimic the minority’s behavior. Likewise, a minority of other-regarding individuals can generate a “cooperative” aggregate outcome if their behavior generates incentives for a majority of self-regarding people to behave cooperatively. Similarly, in strategic games, aggregate outcomes can be either far from or close to Nash equilibrium if players with high degrees of strategic thinking mimic or erase the effects of others who do very little strategic thinking. Recently developed theories of other-regarding preferences and bounded rationality explain these findings and provide better predictions of actual aggregate behavior than does traditional economic theory.

Read more

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Every year renowned literary agent John Brockman asks a group of prominent scientists a question and posts their answers at his web-site The Edge. This years question is “what is your dangerous idea”. In his reply, French neuroscientist Stanislas Dehaene raises the question of neuro-enhancement. As was the case with the Nation article mentioned below, neuro-enhancement is most often viewed as a dubious affair – potentially dangerous and socially unfair. Dehaene, in contrast, is very much in favour of it. We tend to overlook, he writes, just how inherently limited our brain is. If possible, we should do something about this limitation. An excerpt from his reply:

As we gain knowledge of brain plasticity, a major application of cognitive neuroscience research should be the improvement of life-long education, with the goal of optimizing this transformation of our brains. Consider reading. We now understand much better how this cultural capacity is laid down. A posterior brain network, initially evolved to recognize objects and faces, gets partially recycled for the shapes of letters and words, and learns to connect these shapes to other temporal areas for sounds and words. Cultural evolution has modified the shapes of letters so that they are easily learnable by this brain network. But, the system remains amazingly imperfect. Reading still has to go through the lopsided design of the retina, where the blood vessels are put in front of the photoreceptors, and where only a small region of the fovea has enough resolution to recognize small print. Furthermore, both the design of writing systems and the way in which they are taught are perfectible. In the end, after years of training, we can only read at an appalling speed of perhaps 10 words per second, a baud rate surpassed by any present-day modem.

Nevertheless, this cultural invention has radically changed our cognitive abilities, doubling our verbal working memory for instance. Who knows what other cultural inventions might lie ahead of us, and might allow us to further push the limits of our brain biology?

Read all the – many interesting – answers here.

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