Papers for the week, 6/18 – 6/23

Visual analysis of geocoded twin data puts nature and nurture on the map

“…what if the balance of nature and nurture varies depending on where we grow up? Here we use statistical and visual analysis of geocoded data from over 6700 families to show that genetic and environmental contributions to 45 childhood cognitive and behavioral phenotypes vary geographically in the United Kingdom.”

Learning to simulate others’ decisions

“Using behavior, modeling, and fMRI, we show that simulation involves two learning signals in a hierarchical arrangement. A simulated-other’s reward prediction error processed in ventromedial prefrontal cortex mediated simulation by direct recruitment, being identical for valuation of the self and simulated-other. However, direct recruitment was insufficient for learning, and also required observation of the other’s choices to generate a simulated-other’s action prediction error encoded in dorsomedial/dorsolateral prefrontal cortex.”

On the relationship between the ‘default mode network’ and the ‘social brain’

“Social cognition, particularly higher-order tasks such as attributing mental states to others, has been suggested to activate a network of areas at least partly overlapping with the DMN. Here, we explore this claim, drawing on evidence from meta-analyses of functional MRI data and recent studies investigating the structural and functional connectivity of the social brain.”

Punishment can promote defection in group-structured populations

“Pro-social punishment, whereby cooperators punish defectors, is often suggested as a mechanism that maintains cooperation in large human groups…Here we formally investigate how two demographic factors, group size and dispersal frequency, affect selection pressures on pro- and anti-social punishment. Contrary to the suggestions of previous work, we find that anti-social punishment can prevent the evolution of pro-social punishment and cooperation under a range of group structures.”

Direct reciprocity in structured populations

“Direct reciprocity is considered to be a powerful mechanism for the evolution of cooperation, and it is generally assumed that it can lead to high levels of cooperation. Here we explore an open-ended, infinite strategy space, where every strategy that can be encoded by a finite state automaton is a possible mutant.  Surprisingly, we find that direct reciprocity alone does not lead to high levels of cooperation. Instead we observe perpetual oscillations between cooperation and defection, with defection being substantially more frequent than cooperation…Another mechanism for the evolution of cooperation, which has received as much attention, is assortment because of population structure. Here we develop a theory that allows us to study the synergistic interaction between direct reciprocity and assortment.”

Economic incentives and social preferences: substitutes or complements?

“Explicit economic incentives designed to increase contributions to public goods and to promote other pro-social behavior sometimes are counterproductive or less effective than would be predicted among entirely self-interested individuals.  This may occur when incentives adversely affect individuals’ altruism, ethical norms, intrinsic motives to serve the public, and other social preferences. The opposite also occurs—crowding in—though it appears less commonly. In the fifty experiments that we survey, these effects are common, so that incentives and social preferences may be either substitutes (crowding out) or complements (crowding in). We provide evidence for four mechanisms that may account for these incentive effects on preferences: namely that incentives may (i) provide information about the person who implemented the incentive, (ii) frame the decision situation so as to suggest appropriate behavior, (iii) compromise a control averse individual’s sense of autonomy, and (iv) affect the process by which people learn new preferences.”

Emasculation: gloves-off strategy enhances eunuch spider endurance

“Males of sexually cannibalistic spiders commonly mutilate parts of their paired genitals (palps) during copulation…” (!) “We found that by reducing body weight up to 4 per cent in half-eunuchs and 9 per cent in full-eunuchs through emasculation, endurance increases significantly in half-eunuchs (32%) and particularly strongly in full-eunuchs (80%).”

Anterior prefrontal cortex contributes to action selection through tracking of recent reward trends

“A predominant current theory regarding the most anterior sector, the frontopolar cortex (FPC), is that it is involved in exploring alternative courses of action, but the detailed causal mechanisms remain unknown. Here we investigated this issue using the lesion method, together with a novel model-based analysis…Model-based analyses of learning demonstrated a selective deficit in the ability to extrapolate the most recent trend, despite an intact general ability to learn from past rewards. Whereas both brain-damaged and healthy controls used comparisons between the two most recent choice outcomes to infer trends that influenced their decision about the next choice, the group with anterior prefrontal lesions showed a complete absence of this component and instead based their choice entirely on the cumulative reward history.”

Dissociating activity in the lateral intraparietal area from value using a visual foraging task

“…we compared the neural responses of LIP neurons in two subjects with their saccadic behavior and three estimates of stimulus value. These measures were extracted from the subjects’ performance in a visual foraging task, in which we parametrically controlled the number of objects on the screen. We found that the firing rates of LIP neurons did not correlate well with the animals’ behavior or any of our estimated measures of value. However, if the LIP activity was further normalized, it became highly correlated with the animals’ decisions.”

Joint control of Drosophila male courtship behavior by motion cues and activation of male-specific P1 neurons

“Whereas visual information alone is not sufficient to induce courtship behavior in Drosophila melanogaster males, when a subset of male-specific fruitless (fru)- and doublesex (dsx)-expressing neurons that respond to chemosensory cues (P1 neurons) were artificially activated via a temperature-sensitive cation channel (dTRPA1), males followed and extended their wing toward moving objects (even a moving piece of rubber band) intensively. When stationary, these objects were not courted.”

Posts for the week

Bonobo genome sequenced, secrets of sex soon to be unlocked

Beetles are good parents!  And they’re social and talk!

On dopamine and being old

EO Wilson says war is inevitable, that’s just the way we are, someone else disagrees

Vampire electronics on the way

More about our microbiome

On Kuhn.  I wish I could see more of a discussion on the Kuhnian conception of science versus what we actually do in Biology

What men and women focus on when watching porn.  Surprisingly safe for work.

About being an adolescent:

We know from many human functional MRI, or FMRI studies, that the social brain is a network of brain regions that is consistently activated whenever adults think about other people. There are about three different regions in the brain, one in medial prefrontal cortex, and two other regions in the temporal lobe: the posterior-superior temporal sulcus, and the anterior temporal cortex. It doesn’t really matter about the names, but the point is that that network of brain regions in adults is consistently active whenever you think about other people or think about interacting with other people, or think about their mental states or their emotions.

Adolescents use the same network, the social brain network, to a very similar extent, but what seems to happen is that activity shifts from the anterior region, the medial prefrontal cortex region, to the posterior, the anterior temporal cortex or the superior temple sulcus region, as they go through adolescence. In other words, when they’re thinking about other people, adolescents seem to be using this prefrontal cortex, right at the front region, more than adults do, and adults seem to be using the temporal regions more than adolescents do.

How little we know about the neuroscience of fatherhood

Fathers caring for their children is the general rule across most vertebrates; almost all nonmammalian vertebrates use fathers as a prime caregiver.  And yet, the world of neuroscience knows little about paternal care. This is partly because the males of our common laboratory species, the lab mouse and rat, are more likely to eat their young than show any special care for them.  The resulting deficit in knowledge is obvious with any cursory look through a textbook on the neurobiology of parental behavior: after ten chapters detailing maternal behavior, there might be one perfunctory chapter detailing how little we know about paternal behavior.  But here’s a cool fact I learned from one of those chapters: did you know that male Djungarian hamsters assist in delivering pups by tearing away the membranes just after birth.  They play midwife!

It seems like the precise neural circuitry for maternal and paternal care are different; lesioning the amygdala decreases paternal care and increases maternal care.  Likewise, many neurohormones that cause maternal behavior have little effect on males.  But some of these pathways are likely to be the same.  I’ll quickly discuss a paper which describes the influence of the neuropeptides prolactin and oxytocin on paternal care.  Oxytocin is the ‘love hormone’ and strongly stimulates pair-bonding, influences social recognition, and has strong effects on general sociality.  Although it is typically thought of as having a pro-social influence, the reality is a bit more complicated (of course!).  Prolactin is a bit of a sex hormone, providing the body with sexual gratification after intercourse and counteracting the effects of testosterone, estrogen, and dopamine.  It clearly has a stronger social effect as well or I wouldn’t be talking about it in relation to child-rearing!

In order to assess the relationship between these two neuropeptides and fatherhood, Gordon et al. first measured  their concentration in fathers across time and found them to be fairly stable.  When they compared the of these neuropeptides to the propensity of the fathers to play with their children, they found them to be strongly related.  Each were associated with a specific paternal behavior: prolactin with facilitation of a child’s exploratory behavior and oxytocin with how much the fathers matched their facial emotions with that of their children.  Since this is only a correlational study, we cannot say for sure whether or not these neuropeptides are directly causing these behaviors.  However, these are similar to what are seen with maternal behaviors, allowing the researchers to compare their results to the richer maternal literature in the future.  It will be interesting to see if future work can relate receptor variants for these neuropeptides to differences in paternal behavior.  Perhaps we can get a genetics of daddyhood?

Reference

Gordon I, Zagoory-Sharon O, Leckman JF, & Feldman R (2010). Prolactin, Oxytocin, and the development of paternal behavior across the first six months of fatherhood. Hormones and behavior, 58 (3), 513-8 PMID: 20399783

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Papers of the week, 6/10 – 6/17

Joint attention, social-cognition, and recognition memory in adults

“The early emerging capacity for Joint Attention (JA), or socially coordinated visual attention, is thought to be integral to the development of social-cognition in childhood…We tested the validity of the differentiation of IJA [initiating joint attention] and RJA [responding to joint attention] in our paradigm in two studies of picture recognition memory in undergraduate students. Study 1 indicated that young adults correctly identified more pictures they had previously viewed in an IJA condition (67%) than in a RJA (58%) condition, η2 = 0.57. Study 2 controlled for IJA and RJA stimulus viewing time differences, and replicated the findings of Study 1.”

The biological bases of conformity

“We review the relevant literature considering the causation, function, history, and ontogeny of conformity, and describe a computer-based experiment on human subjects that we carried out in order to resolve ambiguities. We found that only when many demonstrators were available and subjects were uncertain was subject behavior conformist. A further analysis found that the underlying response to social information alone was generally conformist. Thus, our data are consistent with a conformist use of social information, but as subjects’ behavior is the result of both social and asocial influences, the resultant behavior may not be conformist.”

Effects of age, sex, and  neuropsychological performance on financial decision-making

“Results indicated that Older participants significantly outperformed Younger participants on a multiple-choice test of acquired financial knowledge. However, after controlling for such pre-existing knowledge, several age effects were observed. For example, Older participants were more likely to make immediate investment decisions, whereas Younger participants exhibited a preference for delaying decision-making pending additional information…In terms of sex differences, Older Males were more likely to pay credit card bills and utilize savings accounts than were Older Females. Multiple positive correlations were observed between Older participants’ financial decision-making ability and performance on neuropsychological measures of non-verbal intellect and executive functioning. Lastly, the ability to justify one’s financial decisions declined with age, among the Older participants.”

Efficient coding and the neural representation of value

“Although normative theories of choice have outlined the theoretical structure of these valuations, recent experiments have begun to reveal how value is instantiated in the activity of neurons and neural circuits. Here, we review the various forms of value coding that have been observed in different brain systems and examine the implications of these value representations for both neural circuits and behavior. In particular, we focus on emerging evidence that value coding in a number of brain areas is context dependent, varying as a function of both the current choice set and previously experienced values. Similar contextual modulation occurs widely in the sensory system, and efficient coding principles derived in the sensory domain suggest a new framework for understanding the neural coding of value.”  By Paul Glimcher, so of course you should read this.

Orbitofrontal cortical activity during repeated free choice

“OFC neurons encode important features of the choice behavior. These features include activity selective for exceptionally long runs of a given choice (stay selectivity) as well as activity selective for switches between choices (switch selectivity). These results suggest that OFC neural activity, in addition to encoding subjective values on a long timescale that is sensitive to satiety, also encodes a signal that fluctuates on a shorter timescale and thereby reflects some of the statistically improbable aspects of free-choice behavior.”

Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the ‘challenge-hypothesis’

“We tested whether the Tsimane, pathogenically stressed forager-horticulturalists of the Bolivian Amazon, would express acute T increases in response to physical competition…Linear mixed-effects models were used to establish that T increased significantly immediately following competition (β = 0.23, p < 0.001), remaining high 1 h later (β = 0.09, p = 0.007); equivalent to 30.1 and 15.5 per cent increases in T, respectively. We did not find larger increases in T among winners (p = 0.412), although T increases were positively associated with self-rated performance (β = 9.07, p = 0.004). These results suggest that despite lower levels of T than US males, Tsimane males exhibit acute increases in T at the same relative magnitude reported by studies in industrialized settings, with larger increases in T for those who report better individual performance.”  I covered this partly in my introduction to testosterone earlier in the week.

Individual plastic responses by males to rivals reveal mismatches between behavior and fitness outcomes

“Behaviour (mating duration) was remarkably sensitive to the level of competition and fully reversible, suggesting that substantial costs arise from the incorrect expression of even highly flexible behaviour. However, changes in mating duration matched fitness outcomes (offspring number) only in scenarios in which males experienced zero then high competition. Following the removal of competition, mating duration, but not offspring production, decreased to below control levels. This indicates that the benefit of increasing reproductive investment when encountering rivals may exceed that of decreasing investment when rivals disappear.”

The dynamics of coordinated group hunting and collective information transfer among schooling prey

“Predators were found to frequently form coordinated hunting groups, with up to five individuals attacking in line formation. Attacks were associated with increased fragmentation and irregularities in the spatial structure of prey groups, features that inhibit collective information transfer among prey. Prey group fragmentation, likely facilitated by predator line formation, increased (estimated) per capita risk of prey, provided prey schools were maintained below a threshold size of approximately 2 m2.”

Aging-related increases in behavioral variability: relations to losses of dopamine D1 receptors

“Increasing ISDs [intraindividual standard deviation] were associated with increasing age and diminished D1 binding in several brain regions (anterior cingulate gyrus, dorsolateral prefrontal cortex, and parietal cortex) for the interference, but not control, condition. Analyses of partial associations indicate that the association between age and IIV in the interference condition was linked to D1 receptor losses in task-relevant brain regions. These findings suggest that dysfunctional DA modulation may contribute to increased variability in cognitive performance among older adults.”

Testosterone: cooperation or competition?

In my last post, I gave an introduction into a couple aspects of testosterone: how it rises and falls, and how it affects decision-making.  I forgot to mention that, neurally, it appears to act substantially through three areas of the brain: the nucleus accumbens, amygdala, and orbitofrontal cortex (OFC).  The nucleus accumbens is a major dopaminergic center, the molecule generally seen as responsible for decision-making and action selection.  Amygdala, as we all know, mediates fear and emotional responses (generally…).  The more interesting area is OFC, which is typically thought to be an area that is involved in self-control.  I couldn’t find many papers that I really wanted to talk about on this aspect of testosterone, so I’ll wait for another day to delve into it.

So let’s look at how testosterone affects social behavior.  In what must have been the Most Fun Study To Participate In Ever, Oxford et al. asked subjects to play Unreal Tournament in teams.  When men are playing the game against other teams, the players that contribute the most show increases in testosterone.  However, when men are forced to play against their own teammates, they have decreased testosterone!  And the subjects who contributed the most to a win showed the largest change.

But if testosterone is increasing during competition against other groups, what affect might it have on social behavior?  Eisenegger et al. used the ultimatum game, where a pair of subjects are given a small amount of money.  One of the subjects then makes an offer of part of the money to the other subject, who can either accept the money or reject it; when the second subject rejects it, neither subject gets any money.  It is well-known that people will generally reject unfair offers.  Following the framework of past studies, female subjects were given either testosterone or placebo and asked to play the game.  They found that subjects who were given testosterone made larger offers than placebo subjects.  Although the authors try to make the claim that this is because being turned down is a ‘status concern’, it could just be because they think that they will make more money that way?  Maybe this is risk-aversion?  I should also note that different study found that subjects given testosterone and asked to be the second subject will also reject more unfair offers.  But the most interesting part about the study is that the subjects who thought that they had received testosterone made much smaller offers – presumably because they already thought they knew what testosterone should do, even though they were wrong!

In a response, van Honk et al. tried using a different game.  He used the ‘public good game’ which is where all players receive 3 moneys, and can contribute some to the public good.  When at least two players contribute to the public good, all players receive 6 moneys.  Note that in this version of the game, with the contribution rate of other players, the expected value is highest when you contribute to the public good.  And subject who have testosterone administered to them give more often to the public good!  So it’s not clear whether they are being more pro-social or just smarter…

The interesting thing about this paper, though is that they also measured the ratio of ring to index finger.  This is a measure of prenatal testosterone exposure, although it doesn’t predict adult levels of testosterone.  Those with a high 2D:4D ratio (ie, those with low maternal testosterone, figure left) are most likely to contribute to the common good, and the less prenatal testosterone, the more of an effect the testosterone given to subjects has.  van Honk et al. suggest that prenatal exposure may change something physically to make subjects more receptive to testosterone, whether it is metabolism or receptor level.  They had found a similar result in a previous study which showed that suspicious individuals didn’t become any more suspicious from testosterone, but the most trusting individuals became much more suspicious when given testosterone (figure right).

The data is a bit hard to interpret, but the general feeling now is that testosterone can act as either a pro-social hormone, or one that makes you more concerned about your social status (egocentrism?).  Although I’d love to give a good clean explanation here, I cannot come up with – and have not yet found – a good unifying framework that unites all the social effects of testosterone .

References

Eisenegger, C., Naef, M., Snozzi, R., Heinrichs, M., & Fehr, E. (2010). Prejudice and truth about the effect of testosterone on human bargaining behaviour Nature, 463 (7279), 356-359 DOI: 10.1038/nature08711

van Honk, J., Montoya, E., Bos, P., van Vugt, M., & Terburg, D. (2012). New evidence on testosterone and cooperation Nature, 485 (7399) DOI: 10.1038/nature11136

Oxford, J., Ponzi, D., & Geary, D. (2010). Hormonal responses differ when playing violent video games against an ingroup and outgroup Evolution and Human Behavior, 31 (3), 201-209 DOI: 10.1016/j.evolhumbehav.2009.07.002

Posts this week

Type of species and type of social network determine how parasites infect a population as it gets larger

Hermit crab social networks!

Social needs sculpt primate faces

Remember: song learning is social learning

Social decision-making across species …and more, but older

Economic Sociology newsletter on New Institutional Economics

A bit late on this one but genoeconomics is an important trend

A really great writeup about serotonin and anorexia

Elephant seal foraging!

When grasshoppers are afraid of spiders, plants decay more slowly.  This is the whole point of this blog: the environment and our interactions with our environment shapes our bodies (and minds!), and the two really cannot be disentangled.

Testosterone: an introduction

Today I want to talk about testosterone.  I had intended for this post to be a short one, but then I kept digging and digging and, well, it turns out that testosterone is a pretty interesting subject.  What I’m going to do today is give a bit of a review on it, and talk about the effect that it has on personal decision-making.  In the next post, I’ll relate testosterone to social decision-making.

Testosterone does a lot of things, and most of them seem to revolve around social status effects – although that simplification may end up making things more confusing.  What testosterone does do is, over time, enhance muscle performance and redistribute immune resources to prepare for injury (remember my post on social status and healing?).  Several things cause increased levels of testosterone, with competition and sex being foremost among them.  This isn’t just physically aggressive competition, either; chess will give you bursts of testosterone.  Historically, calorically stressed populations will see seasonal variations in testosterone levels when men need to suppress aggressive behaviors during child rearing, or get ready for fighting and healing from fighting for status and mates.  But don’t think that testosterone directly will make an individual wildly aggressive.  As Robert Sapolsky notes in The Trouble With Testosterone

Round up some male monkeys…number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 with shit-eating obsequiousness…Take that third monkey and inject him with testosterone.  Inject a ton of it in him…And no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive actions than before…Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence?  Not at all.  He’s still judiciously kowtowing to numbers 1 and 2 but has become a total bastard to numbers 4 and 5.

Males in industrialized societies, however, don’t have any caloric needs causing them to suppress testosterone.  In order to examine testosterone in a more ‘natural’ setting, Trumble et al. turned to ‘pathogenically stressed forager-horticulturalists of the Bolivia Amazon’ (ie, poor and hungry people of the Amazon) who do indeed have lower testosterone levels.  These tribal people were brought together and organized into teams for a soccer tournament.  They found that testosterone was higher after the game in all participants, whether they won or lost.  But pay attention to this: the individuals who thought they performed better had larger increases in testosterone immediately following the game.  An hour later?  The difference disappeared.

It’s this type of effect of confidence that caused (Wright et al. 2012) to examine the effect of testosterone on group collaboration.  They put pairs of female subjects in a room and gave them a visual task where they had to decide which of two sets of bars were brighter.  When the subjects disagreed, they were allowed to discuss it and then one of the pair had to make a decision based on the joint beliefs.  But some of those subjects were given testosterone injections!  And the ones who were given testosterone were more likely to trust their own injections.  Although this seems like a nice result, we don’t really know what is happening during the verbal discussion.  Does the testosteroned subject just verbally browbeat the other subject?  What’s going on there?

So testosterone may act to reinforce egocentric behavior.  How about risk-taking?  That’s a little more complicated.  In a gambling game – with the subject only competing against themselves – (Stanton et al. 2011) showed that high risk taking in a gambling task is associated with high testosterone, but the same group later showed that (Stanton et al. 2011 [2]) there is actually a U-shaped curve.  Subjects with intermediate levels of testosterone are actually risk-averse, while low and high levels are risk-neutral.  This is an important point, and something to keep in mind; often we are not sampling the whole distribution of testosterone levels, and the simple ‘high’ versus ‘low’ dichotomy may be misleading.

So we have seen that testosterone probably goes up and down based on caloric resources and in the presence of competition and mates (or mating).  We’ll conclude next time with a discussion of how testosterone affects sociality, and how things are even more complicated than high/low or U-shaped.

References

Trumble, B., Cummings, D., von Rueden, C., O’Connor, K., Smith, E., Gurven, M., & Kaplan, H. (2012). Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the ‘challenge hypothesis’ Proceedings of the Royal Society B: Biological Sciences, 279 (1739), 2907-2912 DOI: 10.1098/rspb.2012.0455
Wright, N., Bahrami, B., Johnson, E., Di Malta, G., Rees, G., Frith, C., & Dolan, R. (2012). Testosterone disrupts human collaboration by increasing egocentric choices Proceedings of the Royal Society B: Biological Sciences, 279 (1736), 2275-2280 DOI: 10.1098/rspb.2011.2523

Stanton, S., Liening, S., & Schultheiss, O. (2011). Testosterone is positively associated with risk taking in the Iowa Gambling Task Hormones and Behavior, 59 (2), 252-256 DOI: 10.1016/j.yhbeh.2010.12.003

Stanton, S., Mullette-Gillman, O., McLaurin, R., Kuhn, C., LaBar, K., Platt, M., & Huettel, S. (2011). Low- and High-Testosterone Individuals Exhibit Decreased Aversion to Economic Risk Psychological Science, 22 (4), 447-453 DOI: 10.1177/0956797611401752
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Papers of the week, 06/02 – 06/09

I didn’t get to a blog post roundup this week.  But I definitely will this week!  Definitely…  Here we go for the academic papers:

The application of ecological theory toward an understanding of the human microbiome

One review of many on the human microbiome in this week’s Science.  “Each person can be viewed as an island-like “patch” of habitat occupied by microbial assemblages formed by the fundamental processes of community ecology: dispersal, local diversification, environmental selection, and ecological drift. Community assembly theory, and metacommunity theory in particular, provides a framework for understanding the ecological dynamics of the human microbiome, such as compositional variability within and between hosts.”

Friendship networks and social status

“Here we analyze a large collection of such networks representing friendships among students at US high and junior-high schools and show that the pattern of unreciprocated friendships is far from random. In every network, without exception, we find that there exists a ranking of participants, from low to high, such that almost all unreciprocated friendships consist of a lower-ranked individual claiming friendship with a higher-ranked one.”

Whole-brain mapping of direct inputs to midbrain dopamine neurons

“…we comprehensively identified each area’s monosynaptic inputs using the rabies virus. We show that dopamine neurons in both areas integrate inputs from a more diverse collection of areas than previously thought, including autonomic, motor, and somatosensory areas.”  And so on.

Action selection and action value in frontal-striatal ciruits

“Examination of neural activity showed that the representation of the selected action was stronger in lateral prefrontal cortex (lPFC), and occurred earlier in the lPFC than it did in the dorsal striatum (dSTR). In contrast to this, the representation of action values, in both the random and fixed conditions, was stronger in the dSTR. Thus, the dSTR contains an enriched representation of action value, but it followed frontal cortex in action selection.”

Corticosterone predicts foraging behavior and parental care in Macaroni Penguins

Macaroni Penguins!  “Increased corticosterone levels were associated with significantly higher levels of foraging and diving activity and greater mass gain in implanted females. Elevated plasma corticosterone was also associated with an apparent fitness benefit in the form of increased chick mass. Plasma prolactin levels did not correlate with corticosterone levels at any time, nor was prolactin correlated with any measure of foraging behavior or parental care. Our results provide support for the corticosterone-adaptation hypothesis, which predicts that higher corticosterone levels support increased foraging activity and parental effort.”

Structural variations in prefrontal cortex mediate the relationship between early childhood stress and spatial working memory

“Analysis of variations in brain structure revealed that cumulative life stress and spatial working memory were related to smaller volumes in the PFC, specifically prefrontal gray and white matter between the anterior cingulate and the frontal poles. Mediation analyses revealed that individual differences in prefrontal volumes accounted for the association between cumulative life stress and spatial working memory.”

Social status predicts wound healing in wild baboons

“We found no evidence that the high testosterone and intense reproductive effort associated with high rank suppress immune responses. Instead, high-ranking males were less likely to become ill, and they recovered more quickly than low-ranking males, even controlling for differences in age. Notably, alpha males, who experience high glucocorticoids, as well as the highest testosterone and reproductive effort, healed significantly faster than other males, even other high-ranking males.”  But of course, you read about this in my last post.

Iterated prisoner’s dilemma contains strategies that dominate any evolutionary opponent

“It is generally assumed that there exists no simple ultimatum strategy whereby one player can enforce a unilateral claim to an unfair share of rewards. Here, we show that such strategies unexpectedly do exist. In particular, a player X who is witting of these strategies can (i) deterministically set her opponent Y’s score, independently of his strategy or response, or (ii) enforce an extortionate linear relation between her and his scores. Against such a player, an evolutionary player’s best response is to accede to the extortion. Only a player with a theory of mind about his opponent can do better, in which case Iterated Prisoner’s Dilemma is an Ultimatum Game.”  By Freeman Dyson!

How social status determines your health

You wouldn’t think how people perceive you could directly affect your health, would you?  Luckily, science is here to save the day and to tell you, you’re wrong.  A pair of papers published in PNAS in the last month have investigated the interaction between social status and health, and the findings compliment each other rather nicely.

The authors of the first paper tracked baboons over thirty years and made a compelling figure (show at right) showing that low-ranking males are sick more often, and for longer, than high-ranking males.  It has been theorized that the biological effects of high social status – testosterone, high glucocorticoids, high reproductive effort – would reduce health.  After all, if these high-ranking male baboons have to spend all their time and energy making sweet monkey love, there wouldn’t be much energy left over for healing, would there?  However, they found no evidence for this.  In fact, alpha males seemed to heal faster than anyone else.

The authors of the other paper examined the different genes that are regulated in low- and high-status female rhesus monkeys.  The previous paper tracked male animals in the wild, and this one kept female animals in the laboratory.  The authors took blood samples from the monkeys to profile gene expression – though only after dominance order had been established.  It would have been great had they done so before hand to see if there were genes predictive of social status, or if expression changed in any appreciable way.  But no matter.  By using a PCA analysis – basically, finding the combinations of genes that most explained the variance in the behavior – they found that the first principle component was predictive of social status.  This tells us that gene expression is intertwined with your social status.

Almost 1000 genes were found to be associated with rank, 535 of which were more enriched in high-ranking individuals and 452 of which were more enriched in low-ranking individuals.  So a lot is going on in there and getting changed!  Consistent with the previous paper, there was the largest cluster of enriched genes were immune-related.  This included interleukin signaling, T-cell activation, and chemokine/cytokine inflammation.  Perhaps, then, the reason high-ranking males heal faster is because the right immune-related genes were enriched.  But that leaves the question, why should that be so?

The paper included an excel spreadsheet of the enriched genes which can be a bit fun to scroll through; following on something I touched on in the previous post, I expected to find dopamine receptor genes enriched in one of the conditions but I didn’t.  Something to keep in mind.

I guess the moral of story here is: socializing is dangerous.  Or maybe not socializing is dangerous.  Either way, watch out!

References

Archie, E., Altmann, J., & Alberts, S. (2012). Social status predicts wound healing in wild baboons Proceedings of the National Academy of Sciences, 109 (23), 9017-9022 DOI: 10.1073/pnas.1206391109

Tung J, Barreiro LB, Johnson ZP, Hansen KD, Michopoulos V, Toufexis D, Michelini K, Wilson ME, & Gilad Y (2012). Social environment is associated with gene regulatory variation in the rhesus macaque immune system. Proceedings of the National Academy of Sciences of the United States of America, 109 (17), 6490-5 PMID: 22493251

What sleep deprivation and low social status have in common

When you wake up in the morning, you probably don’t always feel 100% on top of things.  Besides feeling drowsy, you make decisions more slowly than you do when you are wide awake.  Things are different!  But maybe that cup of coffee will help you out…

What’s going on in your brain?  It’s been known for a while that adenosine receptors are key to the whole caffeine-waking-you-up thing – caffeine binds one type of adenosine receptor – but there is something more going on.  Volkow et al. had previously implicated a dopamine receptor as somehow changing in sleepy subjects.  They measured receptor activity using a PET scan; this is a technique where a researcher injects a chemical into a subject that binds to specific receptors; when it is bound, it is detectable by the PET scanner.  This binding might increase or decrease depending on the number of receptors (up- or down- regulation) or because the receptors are bound by other things – such different levels of dopamine itself binding the receptors.

Volkow et al. cruelly sleep deprived subjects in order to understand how dopamine was changing by using PET.  What they found is that the longer you are awake, the less the dopamine receptors will bind.  But this could either mean there is more dopamine in the system or that there are fewer dopamine receptors available to be bound.  They also gave some of these subjects provigil, which acts on the dopamine reuptake transporters which carry the dopamine away; when blocked, the dopamine cannot be carried away very effectively and just hangs out, building up.  If the change in binding was due to increased dopamine, the effect of provigil should be different for sleep-deprived subjects than for well-rested patients.  Since this was not the case, Volkow et al. suggest that the number of receptors are themselves getting regulated (though I don’t understand why they don’t know that the dopamine transporters themselves can’t be being regulated instead?).

The receptors that they identified as being important are the D2-type dopamine receptors.  There are many different types of dopamine receptors in the brain, and what exactly each of them is doing is a bit of a mystery.  Broadly speaking, they can be divided into two classes: the D1-type and these D2-type receptors.  D1-type receptors tend to be exciting to the cells in some sense, while the D2-type receptors are somehow inhibitory.

It turns out that D2-type receptors are regulated in other ways; for instance, social status can affect your D2 receptor level.  Simply moving a monkey from living on its own to living in a group will change the receptor level depending on whether it is a high-status animal or a low-status one.  In humans, individuals with low social support show low levels of D2 receptor binding while individuals with high social status show high levels of receptor binding.  This is important for a variety of reasons; most importantly according to papers (ie, it gets the most funding from NIH), individuals with low social support (‘social status’) are most prone to cocaine addiction.  This is true in humans, monkeys, rats, everything.  Perhaps generalized stress results in low levels of D2 receptors?  At the least, we can now all use this as an excuse as to why we make poor decisions when we’re sleepiest.

Photo from.

References

Volkow, N., Tomasi, D., Wang, G., Telang, F., Fowler, J., Logan, J., Benveniste, H., Kim, R., Thanos, P., & Ferre, S. (2012). Evidence That Sleep Deprivation Downregulates Dopamine D2R in Ventral Striatum in the Human Brain Journal of Neuroscience, 32 (19), 6711-6717 DOI: 10.1523/JNEUROSCI.0045-12.2012

Morgan, D., Grant, K., Gage, H., Mach, R., Kaplan, J., Prioleau, O., Nader, S., Buchheimer, N., Ehrenkaufer, R., & Nader, M. (2002). Social dominance in monkeys: dopamine D2 receptors and cocaine self-administration Nature Neuroscience, 5 (2), 169-174 DOI: 10.1038/nn798