Reasoning about our irrational ways

Elizabert Kolbert writes an interesting review in The New Yorker of several books on our irrational economic and political behaviors, the field of behavioral economics. It seems very likely that as politicians and governments become more knowledgeable about the patterns and emotional mechanisms governing our blunders, they will begin to nudge people towards more rational choices. The 'opt out' plans for increasing the numbers of people with health insurance plans or retirement savings are one example of this. Obama's campaign is making very good use of some basic neuro-economics and some of his people are aware of Westin's work (see my July 11 post), as well as Lakoff's (see Jan 31 post). Hillary doesn't seem to have a clue......

A test for Alzheimer's risk

A news piece by Jennifer Couzin in the Feb. 22 Science notes that starting in about a month, for ~$400, you can send a saliva sample to Smart Genetics in Philadelphia for their "Alzheimer's Mirror" test that determines whether you have a variant of the APOE gene that indicates a risk of Alzheimer's that's 3 to 15 times higher than normal. The company plans plan to screen out those who seem emotionally unstable and provide a genetic counseling session by telephone before giving out APOE results.

Not surprisingly many physicians and researchers are expressing reservations about making this gene test widely available. What are the mental health consequences of being told you may get a disease that's neither preventable nor treatable and is invariably fatal? (It's the only genetic information that James Watson, the DNA discoverer who recently had his entire genome sequenced, kept secret.) Would it turn out that people who had this information were more likely experience depression?

An officer at Smart Genetics argues that knowing one is at higher risk might trigger practical responses, including regular memory screenings or making certain financial decisions such as buying long-term care insurance.

Chill out, and your wounds will heal faster.

It is known that anger expression can be associated with increases in cortisol secretion and lowered immune function of the sort seen with other kinds of stress. Gouin et al. at Ohio State Univ. have examined the effect of anger on wound healing by following 98 community volunteers who agreed to receive a standardized blister wound on their non-dominant forearm. They found that wounds of those who expressed little anger or displayed anger in a controlled fashion healed more rapidly than the hotheads. The hotheads exhibited higher cortisol reactivity during the blistering procedure. This enhanced cortisol secretion was in turn related to longer time to heal.

The data show more rapid wound healing in subjects with high anger control.
Measurement of the rate of transepidermal water loss (TEWL) through human skin provides a noninvasive method to monitor changes in the stratum corneum barrier function of the skin. TEWL was measured using a vapor pressure gradient estimation method. TEWL decreased as the barrier was restored; thus, monitoring of TEWL over time allowed objective evaluation of wound healing.

The Fires of Aging

Donna Holmes offers an interesting review with the title of this post, of Caleb Finch's new book "The Biology of Human Longevity." Here are a few edited clips from that review:

Metabolically speaking, we're all on fire. Current thinking in the biology of aging suggests that the normal processes cells use to burn fuel, providing energy for life, indirectly lead to much of the disease and disability that characterize aging in humans and other animals. Chemically unstable by-products of cellular oxidation--especially free oxygen radicals--can initiate the deterioration of cell membranes and macromolecules. As small "hits" causing cellular injury accumulate, the results can range from uncorrected mutations and cancers to forms of tissue damage leading to vascular pathology and Alzheimer's disease.

Oxidative damage remains a central player in the drama Fitch unfolds, but now it shares the stage with several lesser-known, equally important accomplices: inflammation, damage during development, and the hazards of overnutrition.

Finch proposes that increases in brain size and the human life span over the past million years occurred in concert with changing nutritional priorities, slower developmental rates, and a tolerance for inflammation in "dirty, invasive, and stingy" prehistoric environments. The integration of more meat into the human diet, he argues, provided protein needed for larger brains but involved new physiological and genetic trade-offs between fitness and liability for long-term damage. This scenario provides a satisfying rationale for why variants of some genes for metabolizing animal fat that are linked to a human predilection for atherosclerosis, some cancers, and the amyloid plaques characteristic of Alzheimer's disease (such as those of the ApoE gene family) are not shared by our closest primate relatives.

A primer on executive function in the prefrontal cortex

Gilbert and Burgess offer a brief review of our prefrontal brain cortex structures that enable our flexible responses to situations with alternative choices. I think it provides a good look-up reference, and so I want to excerpt a few of the summary figures and text here:

At the heart of most (but not all) theories of executive function is a distinction, or gradation, between routine (or ‘automatic’) and non-routine (or ‘controlled’) processing. Routine processing refers to mental operations that are well rehearsed or overlearned, for example reading out a word. By contrast, non-routine processing most commonly refers to mental operations that are used in situations when there is not a well-established stimulus-response association, or where a behavioural impasse has occurred (for example one notices an error, or realises that one is behaving in a sub-optimal fashion). The term ‘executive functions’ has become synonymous with those behaviours and abilities.

Determining the relative contributions of different frontal subregions to different executive functions is a highly complex matter, both theoretically and methodologically. On current evidence, however, one can make some preliminary suggestions. The figure illustrates some of the major subdivisions of the human PFC, which may be divided into lateral and medial surfaces. On the lateral surface, the PFC may be further subdivided into ventrolateral, dorsolateral, and rostral regions. Although the medial PFC is depicted as a single area in the figure, there is now strong evidence that this part of PFC can also be subdivided both on cytoarchitectonic and functional grounds. The figure shows the lateral surface split into a ventrolateral region (VLPFC), dorsolateral region (DLPFC) and rostral region (RPFC). The medial surface (MPFC) is illustrated as a single region, but recent studies indicate considerable anatomical and functional variation within this region as well. (Click to enlarge)


Ventrolateral PFC (VLPFC) is thought to be involved in comparatively simple tasks, such as short-term maintenance of information that cannot currently be perceived in ‘working memory’ (for example, memorising a phone number you have just been told, before keying the numbers into a telephone). It has also been proposed — although this is controversial — that different parts of the VLPFC are used to store different types of information (for example, the sound of a word versus its meaning). By contrast, dorsolateral PFC (DLPFC) has been most commonly implicated not so much in maintaining information that is no longer available in our environment, but in manipulating that information. For example, although DLPFC is probably not involved in processes such as remembering a telephone number, it does seem to play a role in more difficult tasks, such as dialling the number in reverse order (rearranging the digits that we have just been told). DLPFC has also been suggested to be involved in complex functions such as making plans for the future.

A brain region with strong projections to and from the DLPFC is the anterior cingulate cortex (ACC), part of the medial PFC. One influential theory proposes that this brain region detects the need for control, for example where there is competition between two or more ways of behaving in a certain situation, both of which may be triggered by events in our environment, requiring top-down input to resolve the conflict. It is suggested that the ACC does not itself provide higher-level modulation of lower-level processes, but instead signals to DLPFC when such higher-level modulation is required.

The largest, but most mysterious, sub-region of prefrontal cortex is the rostral PFC (RPFC). As a proportion of whole-brain volume, some have estimated the human RPFC to be twice as large as the corresponding region in the chimpanzee brain. Yet curiously, patients with damage restricted to the RPFC often perform well on standard neuropsychological tests, including ‘classical’ tests of executive function such as the Wisconsin card sorting test. Instead, patients with damage to this region seem to have particular difficulty in real-world ‘multitasking’ situations, such as organising a shopping trip when there are few strict constraints — participants are relatively free to organise their behaviour however they like — but there are also multiple instructions to be remembered, rules to be followed, and potential distractions in the environment. Recent accounts have focused on the role of RPFC in the most high-level human abilities, such as combining two distinct cognitive operations in order to perform a single task, trying to work out what other people are thinking (‘mentalising’), and reflecting on information we retrieve from long-term memory (‘source memory’, for example trying to work out when we last saw a person familiar to us). We recently put forward the unifying hypothesis that this brain region serves as a ‘gateway’ between cognitive processes directed towards current incoming perceptual information, versus information that we generate ourselves. We have also shown (see following figure) by a meta-analysis of functional neuroimaging results that there are distinct functions associated with different parts of the RPFC, with segregation especially between lateral versus medial regions, and between rostral versus caudal regions. (Click to enlarge)

Kahneman on happiness.

An interesting shift in opinion on what we thought we knew about measuring happiness from Nobel laureate Daniel Kahneman:

Ten years ago the generally accepted position was that there is considerable hedonic adaptation to life conditions. The effects of circumstances on life satisfaction appeared surprisingly small: the rich were only slightly more satisfied with their lives than the poor, the married were happier than the unmarried but not by much, and neither age nor moderately poor health diminished life satisfaction. Evidence that people adapt — though not completely — to becoming paraplegic or winning the lottery supported the idea of a "hedonic treadmill": we move but we remain in place. The famous "Easterlin paradox" seemed to nail it down: Self-reported life satisfaction has changed very little in prosperous countries over the last fifty years, in spite of large increases in the standard of living.

Hedonic adaptation is a troubling concept, regardless of where you stand on the political spectrum. If you believe that economic growth is the key to increased well-being, the Easterlin paradox is bad news. If you are a compassionate liberal, the finding that the sick and the poor are not very miserable takes wind from your sails. And if you hope to use a measure of well-being to guide social policy you need an index that will pick up permanent effects of good policies on the happiness of the population.

...an idea that seemed to solve these difficulties: perhaps people's satisfaction with their life is not the right measure of well-being. ..happy people have high aspirations. The aspiration treadmill offered an appealing solution to the puzzles of adaptation: it suggested that measure of life satisfaction underestimate the well-being benefits of life circumstances such as income, marital status or living in California. The hope was that measures of experienced happiness would be more sensitive.

Then after a series of experiments thoroughly refuted this hypothesis, further problems with the original issue:

...recent findings from the Gallup World Poll raise doubts about the puzzle itself. The most dramatic result is that when the entire range of human living standards is considered, the effects of income on a measure of life satisfaction (the "ladder of life") are not small at all. We had thought income effects are small because we were looking within countries. The GDP differences between countries are enormous, and highly predictive of differences in life satisfaction. In a sample of over 130,000 people from 126 countries, the correlation between the life satisfaction of individuals and the GDP of the country in which they live was over .40 – an exceptionally high value in social science. Humans everywhere, from Norway to Sierra Leone, apparently evaluate their life by a common standard of material prosperity, which changes as GDP increases. The implied conclusion, that citizens of different countries do not adapt to their level of prosperity, flies against everything we thought we knew ten years ago. We have been wrong and now we know it. I suppose this means that there is a science of well-being, even if we are not doing it very well.

Your pupils reveal shifts in your perception

Here is an interesting nugget from Christof Koch's laboratory at Cal Tech. When we look at an ambiguous image such as the Necker Cube or the duck/rabbit shown here, our perception switches back and forth between the alternatives.


It turns out that our pupil diameter increases just before the perceptual switch, and predicts its duration. Here is their abstract:

During sustained viewing of an ambiguous stimulus, an individual's perceptual experience will generally switch between the different possible alternatives rather than stay fixed on one interpretation (perceptual rivalry). Here, we measured pupil diameter while subjects viewed different ambiguous visual and auditory stimuli. For all stimuli tested, pupil diameter increased just before the reported perceptual switch and the relative amount of dilation before this switch was a significant predictor of the subsequent duration of perceptual stability. These results could not be explained by blink or eye-movement effects, the motor response or stimulus driven changes in retinal input. Because pupil dilation reflects levels of norepinephrine (NE) released from the locus coeruleus (LC), we interpret these results as suggestive that the LC–NE complex may play the same role in perceptual selection as in behavioral decision making.

Study increases learning less than testing...

Karpicke and Roediger question the common assumption that learning increases as people study and encode material, while measuring that learning by testing does not by itself produce learning. They examined undergraduates tasked with learning the meanings of 40 words in Swahili. Repeated testing of already learned words enhanced long-term recall when assessed 1 week later, whereas repeated studying had no beneficial effects. Testing required the students to retrieve the English-Swahili word associations, which suggests that encoding, although critical for the formation of a memory, may not be sufficient for its retention or consolidation. Their abstract:

Learning is often considered complete when a student can produce the correct answer to a question. In our research, students in one condition learned foreign language vocabulary words in the standard paradigm of repeated study-test trials. In three other conditions, once a student had correctly produced the vocabulary item, it was repeatedly studied but dropped from further testing, repeatedly tested but dropped from further study, or dropped from both study and test. Repeated studying after learning had no effect on delayed recall, but repeated testing produced a large positive effect. In addition, students' predictions of their performance were uncorrelated with actual performance. The results demonstrate the critical role of retrieval practice in consolidating learning and show that even university students seem unaware of this fact.

Bright light and good moods...

We are more agreeable when the light is brighter: here is the abstract, and one figure, from "Exposure to bright light is associated with positive social interaction and good mood over short time periods: A naturalistic study in mildly seasonal people" published in the Journal of Psychology:

Bright light is used to treat winter depression and might also have positive effects on mood in some healthy individuals. We examined possible links between bright light exposure and social interaction using naturalistic data. For 20 days in winter and/or summer, 48 mildly seasonal healthy individuals wore a light meter at the wrist and recorded in real-time their behaviours, mood, and perceptions of others during social interactions. Possible short-term effects of bright light were examined using the number of minutes, within any given morning, afternoon or evening, that people were exposed to light exceeding 1000 lux (average: 19.6 min). Social interactions were labelled as having occurred under conditions of no, low or high bright light exposure. Independent of season, day, time, and location, participants reported less quarrelsome behaviours, more agreeable behaviours and better mood when exposed to high but not low levels of bright light. Given that the effects were seen only when exposure levels were above average, a minimum level of bright light may be necessary for its positive effects to occur. Daily exposure levels were generally low in both winter and summer. Spending more time outdoors and improving indoor lighting may help optimize everyday social behaviour and mood across seasons in people with mild seasonality.

Figure - Quarrelsome behaviours (a) and agreeable behaviours (b) during time periods of no, low, or high levels of bright light exposure. Values are expressed as estimated least squares means of ipsatized frequencies, multiplied by a factor 100. Error bars represent standard errors of the mean. (* Significantly different from social interactions with low bright light exposure.)

Life expectancy increases

Taken from an article by Kirkwood on a systems biology approach to longevity...


The graph shows the life expectancy in the then longest-living country. During the nineteenth and early twentieth centuries, the increase was driven mainly by improvements in sanitation, housing and education, causing a steady decline in early and mid-life mortality, which was chiefly due to infections. This trend continued with the development of vaccines and then antibiotics. By the latter half of the twentieth century, there was little room for further reduction in early and mid-life mortality. The continuing increase is due almost entirely to a new phenomenon: the decline in late-life mortality.

Love speed dating

You may do better in relying on your impression after only 4 minutes of interaction with a potential partner than if you think about it a lot. Here is an engaging essay by Matt Kaplan.

Watching an anesthetic block emotional memory

Here is an intriguing observation by Alkiri et al. We usually recall emotional pictures or events better than neutral ones. They found that low levels of the inhalation anesthetic sevoflurane could block this effect, and with PET imaging found a corresponding suppression of amygdala to hippocampal effective connectivity. Here is their abstract and one summary figure:

It is hypothesized that emotional arousal modulates long-term memory consolidation through the amygdala. Gaseous anesthetic agents are among the most potent drugs that cause temporary amnesia, yet the effects of inhalational anesthesia on human emotional memory processing remain unknown. To study this, two experiments were performed with the commonly used inhalational anesthetic sevoflurane. In experiment 1, volunteers responded to a series of emotional and neutral slides while under various subanesthetic doses of sevoflurane or placebo (no anesthesia). One week later, a mnemonic boost for emotionally arousing stimuli was evident in the placebo, 0.1%, and 0.2% sevoflurane groups, as measured with a recognition test. However, the mnemonic boost was absent in subjects who received 0.25% sevoflurane. Subsequently, in experiment 2, glucose PET assessed brain-state-related activity of subjects exposed to 0.25% sevoflurane. Structural equation modeling of the PET data revealed that 0.25% sevoflurane suppressed amygdala to hippocampal effective connectivity. The behavioral results show that 0.25% sevoflurane blocks emotional memory, and connectivity results demonstrate that this dose of sevoflurane suppresses the effective influence of the amygdala. Collectively, the findings support the hypothesis that the amygdala mediates memory modulation by demonstrating that suppressed amygdala effectiveness equates with a loss of emotional memory.

Figure - The cerebral metabolic effects of 0.25% sevoflurane are shown. (A) Representative high-resolution PET scans. (B) Absolute (mean ± SD) regional metabolic changes (white bars, placebo, no anesthesia; dark bars, 0.25% sevoflurane; marked with * for P less than 0.05). (C) Relative percent decreases of regional metabolism. (D) Regional SPM results of sevoflurane induced metabolic suppression (Upper, sagittal; Lower, axial). E shows the regional thalamic finding (brain center) on a colorized MRI. The SPM effects are significant at P less than 0.001, uncorrected; displayed at P less than 0.005, with a 500-voxel extent.

Languages shape the nuts and bolts of our perception.

The debate over whether language nudges the way we actually see the world is being resolved, and what has been the prevailing dogma - that basic parts of perception are too low-level, too hard-wired, too constrained by the constants of physics and physiology to be affected by language - is breaking down. Lera Boroditsky at Standford comments on this.

I used to think that languages and cultures shape the ways we think. I suspected they shaped they ways we reason and interpret information. But I didn't think languages could shape the nuts and bolts of perception, the way we actually see the world. That part of cognition seemed too low-level, too hard-wired, too constrained by the constants of physics and physiology to be affected by language.

Then studies started coming out claiming to find cross-linguistic differences in color memory. For example, it was shown that if your language makes a distinction between blue and green (as in English), then you're less likely to confuse a blue color chip for a green one in memory. In a study like this you would see a color chip, it would then be taken away, and then after a delay you would have to decide whether another color chip was identical to the one you saw or not.

Of course, showing that language plays a role in memory is different than showing that it plays a role in perception. Things often get confused in memory and it's not surprising that people may rely on information available in language as a second resort. But it doesn't mean that speakers of different languages actually see the colors differently as they are looking at them. I thought that if you made a task where people could see all the colors as they were making their decisions, then there wouldn't be any cross-linguistic differences.

I was so sure of the fact that language couldn't shape perception that I went ahead and designed a set of experiments to demonstrate this. In my lab we jokingly referred to this line of work as "Operation Perceptual Freedom." Our mission: to free perception from the corrupting influences of language.

We did one experiment after another, and each time to my surprise and annoyance, we found consistent cross-linguistic differences. They were there even when people could see all the colors at the same time when making their decisions. They were there even when people had to make objective perceptual judgments. They were there when no language was involved or necessary in the task at all. They were there when people had to reply very quickly. We just kept seeing them over and over again, and the only way to get the cross-linguistic differences to go away was to disrupt the language system. If we stopped people from being able to fluently access their language, then the cross-linguistic differences in perception went away.

I set out to show that language didn't affect perception, but I found exactly the opposite. It turns out that languages meddle in very low-level aspects of perception, and without our knowledge or consent shape the very nuts and bolts of how we see the world.

Watching waves of activity sweep across the brain

This is sensory physiology in the age of YouTube. Peterson and colleagues have used a voltage sensitive dye technique to watch the wave of first sensory area and then motor area excitation that is caused by a tiny deflection of a face whisker of a mouse:

Single brief whisker deflections evoked highly distributed depolarizing cortical sensory responses, which began in the primary somatosensory barrel cortex and subsequently excited the whisker motor cortex. The spread of sensory information to motor cortex was dynamically regulated by behavior and correlated with the generation of sensory-evoked whisker movement. Sensory processing in motor cortex may therefore contribute significantly to active tactile sensory perception.

The video shows the response when a mouses whisker touches an edge:

The movement of the C2 whisker was filmed with a high-speed camera at 500 Hz in an awake behaving mouse during an active touch sequence. Sensorimotor cortex was simultaneously imaged with VSD. At the time indicated by the vertical dotted line, the whisker contacts the object evoking a spreading sensorimotor response, first in S1 and subsequently in M1. The single trial imaging of cortical activity and the behavioral filming are matched frame-by-frame, synchronized through TTL pulses.

Consciousness papers for January

Most downloaded in January 2008 from the ASSC archives:

1. Koriat, A. (2006) Metacognition and Consciousness. In: Cambridge handbook
of consciousness. Cambridge University Press, New York, USA. 1359 downloads
from 27 countries. http://eprints.assc.caltech.edu/175/
2. Sagiv, Noam and Ward, Jamie (2006) Crossmodal interactions: lessons from
synesthesia. In: Visual Perception, Part 2. Progress in Brain Research,
Volume 155. 925 downloads from 19 countries.
http://eprints.assc.caltech.edu/224/
3. Robbins, Stephen E (2007) Time, Form and the Limits of Qualia. Journal of
Mind and Behavior, 28 (1). pp. 19-43. 760 downloads from 14 countries.
http://eprints.assc.caltech.edu/333/
4. Gomes, Gilberto (2005) Is consciousness epiphenomenal? Comment on Susan
Pockett. Journal of Consciousness Studies, 12 (12). pp. 77-79. 739 downloads
from 12 countries. http://eprints.assc.caltech.edu/160/
5. Seth, A.K. and Baars, B.J. (2005) Neural Darwinism and Consciousness.
Consciousness and Cognition, 14. pp. 140-168. 644 downloads from 18
countries. http://eprints.assc.caltech.edu/163/

Your amygdala and your blood pressure

I was intrigued by this article, because it shows what I suppose must be going on in my brain as I notice my blood pressure increasing when my stress system ramps up. (Being an introspective retired professor with sufficient time, I am increasingly noticing small changes in my breathing, heart rate, blood pressure, and relative sympathetic versus parasympathetic activation that accompany changes in context.)

In the article Gianaros et al. use the well-know Stroop color-word interference task to generate stress responses in a group of defined college students. They connect stressor processing with the brainstem cardiovascular control mechanisms regulating blood pressure. People with higher stressor-evoked blood pressure reactivity displayed more activation of the amygdala, especially in the dorsal part that contains the central nucleus. Individuals showing greater blood pressure reactivity also had a lower amygdala gray matter volume, which itself predicted greater amygdala activation. In addition, greater stressor- evoked blood pressure reactivity was correlated with stronger functional connectivity between the amygdala and the pons areas in the brainstem, which is critical for blood pressure control, as well the perigenual anterior cingulate cortex.

The data suggest that the amygdala and some of its projection areas play a role in mediating individual differences in autonomic stress responses and hence vulnerability to psychological stressors.

Figure - A. Greater mean arterial blood pressure (MAP) reactivity varied with greater amygdala activation to the incongruent condition. A, Clusters of the left and right amygdala where MAP reactivity varied with activation after covariate control for sex. Parametric maps are projected onto coronal (top) and axial (bottom) sections of a template derived from study participants. B, MAP reactivity (change from a resting baseline) is shown as a function of mean-centered and standardized amygdala BOLD activation values extracted from the peak voxels of the left (L; open circles, dashed line) and right (R; closed circles, solid line) amygdala clusters profiled in A.

Figure - Greater MAP reactivity varied with stronger positive amygdala-pons functional connectivity. A, Statistical parametric maps derived from an ROI regression analysis identifying pons areas where MAP reactivity varied as a function of connectivity with left (top) and right (bottom) amygdala seed regions. B, MAP reactivity is plotted as a function of amygdala-pons connectivity coefficients for the left (L; open circles, dashed line) and right (R; closed circles, solid line) amygdala.

Oliver Sachs on Migraines

An interesting article on Migraines by Oliver Sachs in the Op-Extra section of The New York Times, focusing on the geometric hallucinations they so often evoke.

...when I first saw photographs of the Alhambra, with its intricate geometric mosaics, I started to wonder whether what I had taken to be a personal experience and resonance might in fact be part of a larger whole, whether certain basic forms of geometric art, going back for tens of thousands of years, might also reflect the external expression of universal experiences. Migraine-like patterns, so to speak, are seen not only in Islamic art, but in classical and medieval motifs, in Zapotec architecture, in the bark paintings of Aboriginal artists in Australia, in Acoma pottery, in Swazi basketry — in virtually every culture. There seems to have been, throughout human history, a need to externalize, to make art from, these internal experiences, from the decorative motifs of prehistoric cave paintings to the psychedelic art of the 1960s. Do the arabesques in our own minds, built into our own brain organization, provide us with our first intimations of geometry, of formal beauty?

Whether or not this is the case, there is an increasing feeling among neuroscientists that self-organizing activity in vast populations of visual neurons is a prerequisite of visual perception — that this is how seeing begins. Spontaneous self-organization is not restricted to living systems — one may see it equally in the formation of snow crystals, in the roilings and eddies of turbulent water, in certain oscillating chemical reactions. Here, too, self-organization can produce geometries and patterns in space and time, very similar to what one may see in a migraine aura. In this sense, the geometrical hallucinations of migraine allow us to experience in ourselves not only a universal of neural functioning, but a universal of nature itself.

Video game addiction, and taking play seriously.

Video games trigger reward and addiction centers of the brain, just like cocaine. Hoeft et. al. at Stanford have compared the activation of these centers in men's and women's brains as they played video games and found them to be more active in male than in female participants. Males showed greater activation and functional connectivity compared to females in the mesocorticolimbic system. The more the men won, the stronger their brain activity. Women's responses were less intense and didn't correlate with winning. This may have something to do with why men seem to become addicted to video games much more easily than women.

There is an interesting and more general article by Robin Henig on play in animals and humans in the New York Times Magazine. The general consensus is that play activity is very important in the development of social intelligence and the ability to respond to rapidly changing situations. It turns out that the rise and decay of play activity in animals corresponds closely to the development curve of the cerebellum, which is important in skilled movements. In one interesting study, experimenters:

...raised 12 female rats from the time they were weaned until puberty under one of two conditions. In the control group, each rat was caged with three other female juveniles. In the experimental group, each rat was caged with three female adults. Pellis knew from previous studies that the rats caged with adults would not play, since adult rats rarely play with juveniles, even their own offspring. They would get all the other normal social experiences the control rats had — grooming, nuzzling, touching, sniffing — but they would not get play... (in) the rats raised in a play-deprived environment, they found a more immature pattern of neuronal connections in the medial prefrontal cortex... less selective pruning of cells and a more tangled, immature medial prefrontal cortex in play-deprived rats might mean that the rat will be less able to make subtle adjustments to the social world.

There are numerous theories about the function of play. It doesn't seem unreasonable that that the fragmentary, disorderly, unpredictable, exaggerated, improvised, vertiginous, and nonsensical nature of play trains the brain allows for a wider behavioral repertory and perhaps more competence in responding to novel or unforeseen situations.

Killer Instincts.

Dan Jones writes a news feature in Nature on neuroscientific and evolutionary perspectives on homicide, mainly carried out by men. Here are some selected chunks:

Men are not just more likely to kill other people than women are, they are also more likely to do so in groups ...Humans are not the only primates to form coalitions that kill members of neighbouring communities. ...five long-term study sites dotted around Africa have seen murderous 'gang violence' in chimpanzees...Wilson and Muller have compared death rates from conflict between groups of chimps in the five long-term study sites with data for inter-group human conflicts in numerous subsistence-farmer and hunter–gatherer societies...Overall, humans and chimpanzees showed comparable levels of violent death from aggression between groups...however, chimps display within group aggression and killing behaviour 200 times more frequently that aboriginal human groups...this prosocial lack of violence looks like a fundamental aspect of human nature — the human ability to generate in-group amity often goes hand in hand with out-group enmity...Choi and Bowles have produced models in which altruism and war co-evolve, promoting conflict between groups and greater harmony within them.

A decline in inter-personal violence (as opposed to inter-group war) can be seen over the shorter timescale and narrower field of modern European history. Eisner has documented a trend of declining homicide rates estimated from historical records left by coroners, royal courts and other official sources spanning Europe from the twelfth century to the modern day. After rising from an average of 32 homicides per 100,000 people per year in the thirteenth and fourteenth centuries to 41 in the fifteenth, the murder rate has steadily dropped in every subsequent century, to 19, 11, 3.2, 2.6 and finally 1.4 in the twentieth century...a few centuries is too short a time for evolution to have shaped human nature much... A part of the answer that is consistent with an evolutionary approach is a long-term reduction in inequalities of life circumstances and prospects.

Human and Animal Math

Michael Beran writes a brief review of the evolutionary and developmental foundations of mathematics. Humans and other higher animals are born with a dedicated systems for numerical processing.