Highjacked brain fallacy, and free will illusion going mainstream.

In a series of previous posts on MindBlog I have enjoyed following the continuing back and forth over free will and neuroscience,and my own sentiments are clearly revealed in my introductory web/lecture listed in the column to your left ("The I Illusion"). A raft of books on this subject has recently appeared, an example being Eagleman's "Incognito: Secret Lives of the Brain" as well as several mentioned in a recent Huffington Post essay by Victor Strenger. An interesting variation on the free will question is provided by O'Connor's discussion of a popular analogy that clouds our discussion of addiction, i.e. the portrayal of addition as a disease (not subject to our willful control, thus not the responsibility of the victim) rather than a choice.

In the “hijacked” view of addiction, the brain is the innocent victim of certain substances — alcohol, cocaine, nicotine or heroin, for example — as well as certain behaviors like eating, gambling or sexual activity...drugs like alcohol and cocaine and behaviors like gambling light up the brain’s pleasure circuitry, often bringing a burst of euphoria. Other studies indicate that people who are addicted have lower dopamine and serotonin levels in their brains, which means that it takes more of a particular substance or behavior for them to experience pleasure or to reach a certain threshold of pleasure.

However,

"A hijacker comes from outside and takes control by violent means. A hijacker takes a vehicle that is not his; hijacking is always a form of stealing and kidnapping...The analogy of addiction and hijacking involves the same category mistake as the money switched from hand to hand...It might be tempting to claim that in an addiction scenario, the drugs or behaviors are the hijackers. However, those drugs and behaviors need to be done by the person herself...In the usual cases, an individual is the one putting chemicals into her body or engaging in certain behaviors in the hopes of getting high...There is a kind of intentionality to hijacking that clearly is absent in addiction...Addiction develops over time and requires repeated and worsening use...If we think, however, of addiction as involving both choice and disease, our outlook is likely to become more nuanced.

Linking choice and responsibility is right in many ways, so long as we acknowledge that choice can be constrained in ways other than by force or overt coercion. There is no doubt that the choices of people progressing to addiction are constrained; compulsion and impulsiveness constrain choices. Many addicts will say that they choose to take that first drink or drug and that once they start they cannot stop. A classic binge drinker is a prime example; his choices are constrained with the first drink. He both has and does not have a choice. (That moment before the first drink or drug is what the philosopher Owen Flanagan describes as a “zone of control.”) But he still bears some degree of responsibility to others and to himself...Addicts are neither hijackers nor victims. It is time to retire this analogy.

Exercise bad for you?

My almost religious devotion to exercise has been slightly nudged by this piece by Gina Kolata pointing to a study by Bouchard et al., who do a rather thorough exercise study involving 1,687 people to find that

...about 10 percent actually got worse on at least one of the measures related to heart disease: blood pressure and levels of insulin, HDL cholesterol or triglycerides....But counterbalancing the 10 percent who got worse were about the same proportion who had an exaggeratedly good response on at least one measure. Others had responses ranging from little or no change up to big changes, seen in about 10 percent, where risk factor measurements improved anywhere from 20 percent to 50 percent.

The burdens of being a biped

Given my current preoccupation with my failing 70 year old knee joints, I was drawn to a brief piece by Elizabeth Pennisi with the title of this post.  Here I give a summary graphic and a few clips of her discussion:

...a number of musculoskeletal issues are traceable to our past, in particular to the switch to walking upright more than 7 million years ago…Shifting from a four-legged support system to a two-legged one put extra stress on the legs and vertebrae. Adaptations in the feet, knees, hips, pelvis, and spine accommodate these forces, but at a cost…vertebrae that break more easily, weaker bones, and feet prone to heel spurs and sprained ankles…A brief tour of the body reveals a number of design flaws, the legacy of our past…

Spine. Back pain is the leading health complaint in the United States. In dogs, horses, and even chimpanzees, the backbone is a series of vertebrae neatly stacked and evenly spaced to form a relatively stiff, gently curving beam…the human spine… is highly flexible and can even bend backward..this flexibility creates wear and tear on joint surfaces and predisposes us to osteoarthritis…One type of break, called spondylolysis, affects about 6% of the U.S. population and is a leading cause of lower-back pain in teenage athletes. In this condition, the neural arch - a triangle of bone that surrounds the spinal cord - detaches from the rest of its vertebra, allowing the spine to slip forward relative to the back of the pelvis, pinching nerves and causing pain…the problem lies in inadequate spacing between the joints connecting the vertebrae.

Feet. To cope with the added load on just two feet, the foot evolved a shock-absorbing arch by bringing what was a grasping big toe into line with the other toes. When that arch fails to form fully, as in people with flat feet, fatigue fractures can result.

Fragile bones. The added load on two feet also caused knee and hip joints to expand, creating more surface area to absorb foot-fall forces. But the joints—and vertebrae as well—evolved to be bigger by enlarging the spongy, inner bone and thinning the hard, outer bone. As a result, human bones are less dense than those of other primates. Bone...loses mass during adulthood. With humans having ever longer life spans, bones, particularly vertebrae, may become fragile and break spontaneously.

Bipedality leaves its mark in other parts of our bodies, too, for example in the difficulty of childbirth and in our vulnerability to rotator cuff injuries of the shoulder. loses mass during adulthood. With humans having ever longer life spans, bones, particularly vertebrae, may become fragile and break spontaneously.

A musical offering.

As has been my custom, I post on this blog piano video-recordings that I have recently made, this being the Chopin Nocturne in C# Minor that I played at a house concert on May 27, and subsequently recorded on June 10.

Skin Pics

One frequently comes across amazing images in cell biology. This time I felt like passing some on to readers.

The science of gaydar

Yet another study suggesting that we have an ability (if not a proficiency) to correctly judge the sexual orientation of others about 60% of the time, significantly great than chance. This piece in the New York Times points to work by Tabak and Zayas:

Research has shown that people are able to judge sexual orientation from faces with above-chance accuracy, but little is known about how these judgments are formed. Here, we investigated the importance of well-established face processing mechanisms in such judgments: featural processing (e.g., an eye) and configural processing (e.g., spatial distance between eyes). Participants judged sexual orientation from faces presented for 50 milliseconds either upright, which recruits both configural and featural processing, or upside-down, when configural processing is strongly impaired and featural processing remains relatively intact. Although participants judged women’s and men’s sexual orientation with above-chance accuracy for upright faces and for upside-down faces, accuracy for upside-down faces was significantly reduced. The reduced judgment accuracy for upside-down faces indicates that configural face processing significantly contributes to accurate snap judgments of sexual orientation.

Brain correlates of resting, alert, and meditation states.

Posner and colleagues do a nice review of neural correlates of establishing, maintaining, and switching brain states.  I thought I would pass on a few chunks from their article describing the alert state and the meditation state:

The three brain states are compared in Table 1.

The meditation state differs from the alert state induced by a warning signal in several crucial ways. First, the alert state can be induced by the simple instruction to expect a target, without requiring any practice, whereas the meditation state requires specific instruction and practice. Second, the alert state requires an external target, whereas the meditation state may not involve a target event. Third, the alert state involves primarily the neuromodulator NE, whereas dopamine (DA) has often been shown to be important to the meditation state. Finally, the alert state involves a reduction in ACC activity, likely in order to keep the mind clear to perceive and respond quickly to the target. The meditation state, however, shows increased ACC activity that serves to regulate mind wandering. As mentioned previously, Five days of integrative mind-body training (IBMT) increases brain activity in the ACC, insula, and striatum. One month of IBMT improves white matter connectivity between the ACC, striatum, and other regions. Based on these results and related work, we propose the insula, ACC, and stiatum (IAS) as key neural correlates of changing brain states (Figure 2).

Because of its role in attention and self-regulation, we hypothesize that the ACC is involved in maintaining a state by reducing conflict with other states; the insula serves a primary role in switching between states, and the striatum is linked to the reward experience and formation of habits needed to make maintenance easier. The insula and ACC work together to support the role of the autonomic nervous system in maintaining the meditation state.

Your great grandparent's experience might have altered your stress response.

This fascinating nugget from Crews et a. (open access) adds to accumulating evidence on the importance of experience induced modification of our genomes that can be passed between generations. (The experiments are on mice, because obviously you don't do this kind of study directly on humans.)

Ancestral environmental exposures have previously been shown to promote epigenetic transgenerational inheritance and influence all aspects of an individual’s life history. In addition, proximate life events such as chronic stress have documented effects on the development of physiological, neural, and behavioral phenotypes in adulthood. We used a systems biology approach to investigate in male rats the interaction of the ancestral modifications carried transgenerationally in the germ line and the proximate modifications involving chronic restraint stress during adolescence. We find that a single exposure to a common-use fungicide (vinclozolin) three generations removed alters the physiology, behavior, metabolic activity, and transcriptome in discrete brain nuclei in descendant males, causing them to respond differently to chronic restraint stress. This alteration of baseline brain development promotes a change in neural genomic activity that correlates with changes in physiology and behavior, revealing the interaction of genetics, environment, and epigenetic transgenerational inheritance in the shaping of the adult phenotype. This is an important demonstration in an animal that ancestral exposure to an environmental compound modifies how descendants of these progenitor individuals perceive and respond to a stress challenge experienced during their own life history.

MindBlog's other lives

This post is sharing with readers two aspects of Deric's private life.  I studied visual transduction over a 36 year period (1960-1996), and on Saturday May 26, near a 70th birthday in May, my former students  gathered in Madison Wisconsin (one flying from Japan for the weekend!) for a laboratory reunion.  Several former Ph.D. or postdoctoral students now head their own laboratories, are department chairs, have chair professorships, or have won academic prizes.  In preparation for the reunion, I prepared a brief web history of the laboratory, and pictures of the reunion can be found here.

On the next day, Sunday May 27,  my partner Len (on right in the picture below) and I hosted a Social/Musical at our Twin Valley home (an 1860 stone schoolhouse converted to a residence) that was attended by friends as well as many who were at the laboratory reunion.  Music selections were from the romantic literature, by Chopin, Brahms, Faure, and Debussy. Pictures of that occasion can be found here.  Included in this post is a video of the Chopin C Minor Nocture played at the Social, recorded this past Saturday. I hope to do video recordings of several of the pieces played in the next period of time.)

   

Different sorts of suspicion - brain correlates

Bhatt et al. (open access) show brain correlates of the distinction between suspicion based on a person’s general beliefs about people in the world and the situation at hand, versus suspicion that is generated by the behavior of other people:

Humans assess the credibility of information gained from others on a daily basis; this ongoing assessment is especially crucial for avoiding exploitation by others. We used a repeated, two-person bargaining game and a cognitive hierarchy model to test how subjects judge the information sent asymmetrically from one player to the other. The weight that they give to this information is the result of two distinct factors: their baseline suspicion given the situation and the suspicion generated by the other person’s behavior. We hypothesized that human brains maintain an ongoing estimate of the credibility of the other player and sought to uncover neural correlates of this process. In the game, sellers were forced to infer the value of an object based on signals sent from a prospective buyer. We found that amygdala activity correlated with baseline suspicion, whereas activations in bilateral parahippocampus correlated with trial-by-trial uncertainty induced by the buyer’s sequence of suggestions. In addition, the less credible buyers that appeared, the more sensitive parahippocampal activation was to trial-by-trial uncertainty. Although both of these neural structures have previously been implicated in trustworthiness judgments, these results suggest that they have distinct and separable roles that correspond to their theorized roles in learning and memory.

Why the liberals lost Wisconsin, and Obama may lose.

Last Tuesday the liberal bubble of Madison Wisconsin that I live in got reminded of what the rest of the state (and the U.S.) is really like:

I think this graphic from an article by Jonathan Haidt (whose book "The Righteous Mind" I'm reading, and strongly recommend you read) gives the most important part of the story. The conservative stance appeals to five of our evolved moral emotions, the liberal stance to only two.

Deep brain stimulation, fear extinction, and OCD suppression

Interesting work from Rodriguez-Romaguera et al. (open access):

Deep brain stimulation (DBS) of the ventral capsule/ventral striatum (VC/VS) reduces symptoms of intractable obsessive-compulsive disorder (OCD), but the mechanism of action is unknown. OCD is characterized by avoidance behaviors that fail to extinguish, and DBS could act, in part, by facilitating extinction of fear. We investigated this possibility by using auditory fear conditioning in rats, for which the circuits of fear extinction are well characterized. We found that DBS of the VS (the VC/VS homolog in rats) during extinction training reduced fear expression and strengthened extinction memory. Facilitation of extinction was observed for a specific zone of dorsomedial VS, just above the anterior commissure; stimulation of more ventrolateral sites in VS impaired extinction. DBS effects could not be obtained with pharmacological inactivation of either dorsomedial VS or ventrolateral VS, suggesting an extrastriatal mechanism. Accordingly, DBS of dorsomedial VS (but not ventrolateral VS) increased expression of a plasticity marker in the prelimbic and infralimbic prefrontal cortices, the orbitofrontal cortex, the amygdala central nucleus (lateral division), and intercalated cells, areas known to learn and express extinction. Facilitation of fear extinction suggests that, in accord with clinical observations, DBS could augment the effectiveness of cognitive behavioral therapies for OCD.

Embodied metaphors and creative acts

K.-y. Leung et al. do a series of studies that suggest that embodiment of metaphors for creativity promotes creative problem solving. Given that across cultures and languages (e.g., English, Korean, Hebrew, and Chinese), metaphors associate creativity with bilateral physical orientations (thinking about a problem “on one hand” and then “on the other hand”), a first study probed divergent thinking (fluency, flexibility, and originality) by asking participants to imagine multiple uses for a university building complex while gesturing with their right hand towards a wall. During a second trial, control participants generated additional ideas while raising the same hand they had raised during the first trial; participants in the experimental condition, however, switched hands by holding their left hand toward the wall and their right hand behind their back while they generated additional ideas (participants were not aware that they would have to generate answers to the same question on both trials until the second trial began.) The experimental subjects who changed hands generated more ideas, which were also more flexible and original.

A second two part experiment looked at the "think outside of the box" metaphor by seating participants inside or outside of a 5x5 ft. box, who carried out a convergent thinking task (think of a word that is related to three cue words. For example, “measure,” “worm,” and “video” might elicit the fourth word “tape”). Participants who completed such a remote associates test while they were physically outside the box generated more correct answers. In a variation on the box theme, divergent thinking was then probed by noting the effect of having participants physically embody a box by walking in a fixed, rectangular path. Participants who could move freely were more creative in imagining identities of ambiguous objects.

Two further studies dealt with the “putting two and two together” metaphor (by noting the effect of physically moving blocks on convergent thinking), and imagining bodily motions in a virtual world similar to those of physically enacting such metaphors (as in the first and second experiments).

Here is their abstract:

Creativity is a highly sought-after skill. Prescriptive advice for inspiring creativity abounds in the form of metaphors: People are encouraged to “think outside the box,” to consider a problem “on one hand, then on the other hand,” and to “put two and two together” to achieve creative breakthroughs. These metaphors suggest a connection between concrete bodily experiences and creative cognition. Inspired by recent advances in the understanding of body-mind linkages in the research on embodied cognition, we explored whether enacting metaphors for creativity enhances creative problem solving. Our findings from five studies revealed that both physical and psychological embodiment of metaphors for creativity promoted convergent thinking and divergent thinking (i.e., fluency, flexibility, or originality) in problem solving. Going beyond prior research, which focused primarily on the kind of embodiment that primes preexisting knowledge, we provide the first evidence that embodiment can also activate cognitive processes that facilitate the generation of new ideas and connections.

The power of network visualization.

A colleague of mine in the campus Chaos seminar pointed us to this 10 minute talk, which I found very engaging. It is given by Manuel Lima, who is senior UX design lead at Microsoft Bing:

Unconscious actions of testosterone

Here is an interesting observation from Terburg et al.:

Throughout vertebrate phylogeny, testosterone has motivated animals to obtain and maintain social dominance—a fact suggesting that unconscious primordial brain mechanisms are involved in social dominance. In humans, however, the prevailing view is that the neocortex is in control of primordial drives, and testosterone is thought to promote social dominance via conscious feelings of superiority, indefatigability, strength, and anger. Here we show that testosterone administration in humans prolongs dominant staring into the eyes of threatening faces that are viewed outside of awareness, without affecting consciously experienced feelings. These findings reveal that testosterone motivates social dominance in humans in much the same ways that it does in other vertebrates: involuntarily, automatically, and unconsciously.

Quantitative analysis of language evolution.

Modern computation techniques and the mass digitization of books have made possible the systematic analysis of one of humankind's most important cultural artifacts, its languages. A analysis by Hughes et al. is quite different from studies in the dating of literary works, the analysis of the coarse-grained structure of literary history (and the evolution of genre), and most notably, a recent analysis of Google Books that examined temporal trends in content-word usage. (One of the co-authors of the study is a polymath, David Krakauer, who recently become Director of our Wisconsin Institute of Discovery here at the University of Wisconsin and is also Co-Director of its Center for Complexity and Collective Computation). Hughes et al. focus on the usage of content-free words as the basis of a first large-scale study of the similarity structure of literary style. Content-free words are the “syntactic glue” of a language: They are words that carry little meaning on their own but form the bridge between words that convey meaning. Their joint frequency of usage is known to provide a useful stylistic fingerprint for authorship, and thus suggests a method of comparing author styles. Their dataset was a subset of 537 authors in the Project Gutenberg database composed of those who wrote after the year 1550, had at least five works in English in the Project Gutenberg collection, and for whom birth and death date information was available. The primary results of the analysis are that time provides the most coherent means of clustering work and that a trend of diminishing stylistic influence is observed as one moves forward in time. Such a finding is consistent with a simple evolutionary model for stylistic influence, which assumes that imitation attends preferentially to contemporary authors. The authors uncover quantitative support of the previously purely anecdotal notion of a literary “style of a time.” They note that their findings suggest the utility and perhaps the creation of a new field of stylometric analysis in culturomics. Here is their abstract:

Literature is a form of expression whose temporal structure, both in content and style, provides a historical record of the evolution of culture. In this work we take on a quantitative analysis of literary style and conduct the first large-scale temporal stylometric study of literature by using the vast holdings in the Project Gutenberg Digital Library corpus. We find temporal stylistic localization among authors through the analysis of the similarity structure in feature vectors derived from content-free word usage, nonhomogeneous decay rates of stylistic influence, and an accelerating rate of decay of influence among modern authors. Within a given time period we also find evidence for stylistic coherence with a given literary topic, such that writers in different fields adopt different literary styles. This study gives quantitative support to the notion of a literary “style of a time” with a strong trend toward increasingly contemporaneous stylistic influence.

It seems a bit amazing that their analysis of the use of 307 content-free words that included prepositions, articles, conjunctions, “to be” verbs, and some common nouns and pronouns allowed them to cluster authors in time and by narrative theme, and that content-free word frequencies were found to be fairly faithfully transmitted among authors of a similar period, even when imitation at this level of textual resolution seems to be out of the question. Moving into the present, this imitation becomes increasingly localized to our contemporaries. Further edited clips:

We propose that for the earliest periods in our dataset, and through the early modern period, the number of published works remained relatively low. This allowed authors to have sufficient time to sample (read) very broadly from the full range of historically published works. Common phrasing, and norms of syntax and grammar, remain relatively unchanged for long periods of time. This generates decay rates in similarity as a function of temporal distance that are not significantly different from the average, because authors are influenced by models distributed uniformly in time. However, for more recent authors, the number of possible choices of books to read has increased dramatically, and with a finite amount of time, a subset of these works must be chosen, leading to rather heterogeneous reading patterns and a greater overall diversity of authored works. The pattern accelerates in the later modern period, with even more authors to choose from and selection dominated by contemporaneous authors. This suggests a simple evolutionary model for patterns of influence.

The negative influence of authors from a preceding generation in the period 1907–1952 could be explained by the Modernist movement. Modernist authors, who are contained within this time period, display a radical shift in style as they reject their immediate stylistic predecessors yet remain a part of a dominant movement that included many of their contemporaries. The contemporary influence of writing programs and their often close readings of contemporary works and feedback (sometimes called “reflexive modernism”) has also been suggested to contribute to this effect. The overall pattern that we find is that the stylistic influence of the past is diminishing at an increasing rate, which suggests that style itself is evolving at an accelerating pace.

The patterns of influence are a first discovery from the corpus. Implicit in this is a temporal clustering of similarity and quantitative support for the qualitative suggestions of a notion of a “style of a time.” It is also worth noting that the implicit temporal clustering of similarity is not an exclusively temporal phenomenon. A network representation of the authors reveals evidence of thematic clustering as well. Examples include interesting groupings of English poets and playwrights, military leaders, and a collection of important naturalists, social thinkers, and historians. This is suggestive and supportive of the hypothesis that word frequencies are not only typical of a given time but also of a field of inquiry. Historians and naturalists do not only write about different topics, they write about them differently. Taken together with the patterns of decay in influence this suggests that whereas authors of the 18th and 19th centuries continued to be influenced by previous centuries, authors of the late 20th century are strongly influenced by authors from their own decade. The so-called “anxiety of influence”, whereby authors are understood in terms of their response to canonical precursors, is becoming an “anxiety of impotence,” in which the past exerts a diminishing stylistic influence on the present. These results are consistent with many complex, scaling phenomena such as those found in urban and technological systems, where there has been an accelerating rate of change into the present. This is a rather intriguing pattern of short-term cultural evolution that is different from the constant rates of change reported for names and pottery or the reduced rates of lexical substitution of frequently used words over thousands of years. Further analysis will elucidate not only the transmission mechanisms generating temporally localized styles but additional stylistic factors that help differentiate the style of one author from that of another.

Social jetlag and obesity.

Roenneberg et al. do an epidemiological study, showing that, beyond sleep duration, the difference between natural circadian sleep rhythm and the actual times of sleep people observe (social jetlag) is associated with increased body mass index. They suggest that living “against the clock” may be a factor contributing to the modern epidemic of obesity. (But... it seems to me people were doing this before the obesity epidemic was noted. Most experts attribute the epidemic to increased physical inactivity and abundance of cheap highly caloric foods.) Here is their summary and abstract:

-In 70% of the population, biological and social clocks differ by >1 hr (social jetlag) -Social jetlag is a predictor of BMI, especially for overweight individuals -The decrease of sleep duration over the past decade concerns only workdays -Individuals are progressively exposed to decreasing light, and their chronotypes delay

Abstract

Obesity has reached crisis proportions in industrialized societies. Many factors converge to yield increased body mass index (BMI). Among these is sleep duration. The circadian clock controls sleep timing through the process of entrainment. Chronotype describes individual differences in sleep timing, and it is determined by genetic background, age, sex, and environment (e.g., light exposure). Social jetlag quantifies the discrepancy that often arises between circadian and social clocks, which results in chronic sleep loss. The circadian clock also regulates energy homeostasis, and its disruption—as with social jetlag—may contribute to weight-related pathologies. Here, we report the results from a large-scale epidemiological study, showing that, beyond sleep duration, social jetlag is associated with increased BMI. Our results demonstrate that living “against the clock” may be a factor contributing to the epidemic of obesity. This is of key importance in pending discussions on the implementation of Daylight Saving Time and on work or school times, which all contribute to the amount of social jetlag accrued by an individual. Our data suggest that improving the correspondence between biological and social clocks will contribute to the management of obesity.

Social interactions prime us for motor empathy or resonance.

Hogeveen and Obhi1 find that recent experience tunes our mirroring systems to particular agent types. A bit from their introduction, followed by the abstract:

Detecting and responding to biological stimuli such as predators or potential mates is a fundamental and adaptive capability, supported by rain areas such as the posterior superior temporal sulcus (pSTS) which is biased for processing biological motion. The pSTS and the parietofrontal mirror system form part of a wider action observation network (AON), which is thought to underlie many social abilities. Motor resonance (MR) is the activation of matching motor representations during observation of action(s) made by others, and could index mirror activity within the wider AON.

Understanding the neural basis of social behavior has become an important goal for cognitive neuroscience and a key aim is to link neural processes observed in the laboratory to more naturalistic social behaviors in real-world contexts. Although it is accepted that mirror mechanisms contribute to the occurrence of motor resonance (MR) and are common to action execution, observation, and imitation, questions remain about mirror (and MR) involvement in real social behavior and in processing nonhuman actions. To determine whether social interaction primes the MR system, groups of participants engaged or did not engage in a social interaction before observing human or robotic actions. During observation, MR was assessed via motor-evoked potentials elicited with transcranial magnetic stimulation. Compared with participants who did not engage in a prior social interaction, participants who engaged in the social interaction showed a significant increase in MR for human actions. In contrast, social interaction did not increase MR for robot actions. Thus, naturalistic social interaction and laboratory action observation tasks appear to involve common MR mechanisms, and recent experience tunes the system to particular agent types.

Serotonin modulates reward value in our decision making.

Seymour et al. find further behavioral and neural evidence that serotonin modulates (is necessary for) distinct behavioral and anatomical components of decision-making. Most surprising is their observation of a strongly positive dependence of reward outcome value on serotonin signaling, with corresponding cue-value-related activity in vmPFC and prediction-error-related activity in dorsolateral putamen (for errors). This value-dependent effect was behaviorally and anatomically distinct from an effect of serotonin on behavioral flexibility, as indicated by choice perseveration. Here is their abstract:

Establishing a function for the neuromodulator serotonin in human decision-making has proved remarkably difficult because if its complex role in reward and punishment processing. In a novel choice task where actions led concurrently and independently to the stochastic delivery of both money and pain, we studied the impact of decreased brain serotonin induced by acute dietary tryptophan depletion. Depletion selectively impaired both behavioral and neural representations of reward outcome value, and hence the effective exchange rate by which rewards and punishments were compared. This effect was computationally and anatomically distinct from a separate effect on increasing outcome-independent choice perseveration. Our results provide evidence for a surprising role for serotonin in reward processing, while illustrating its complex and multifarious effects.

The neurogenetics of nice.

Interesting observations from Poulin et al...They note that all prosocial acts require people to contend with concerns about potential exploitation or loss of resources (i.e., threats). If oxytocin and vasopressin moderate responses to such threats, they may influence a wide variety of prosocial behaviors, including those outside a laboratory context. It is known that oxytocin administration reduces amygdalar reactivity to negative stimuli,and amygdalar reactivity, in turn, mediates oxytocin’s effects on generosity in the context of an economic game. The G/G genotype of the rs53576 single-nucleotide polymorphism (SNP) for OXTR also predicts lower cardiovascular reactivity to startle anticipation than do the A/A and A/G genotypes. Here is their abstract:

Oxytocin, vasopressin, and their receptor genes influence prosocial behavior in the laboratory and in the context of close relationships. These peptides may also promote social engagement following threat. However, the scope of their prosocial effects is unknown. We examined oxytocin receptor (OXTR) polymorphism rs53576, as well as vasopressin receptor 1a (AVPR1a) polymorphisms rs1 and rs3 in a national sample of U.S. residents (n = 348). These polymorphisms interacted with perceived threat to predict engagement in volunteer work or charitable activities and commitment to civic duty. Specifically, greater perceived threat predicted engagement in fewer charitable activities for individuals with A/A and A/G genotypes of OXTR rs53576, but not for G/G individuals. Similarly, greater perceived threat predicted lower commitment to civic duty for individuals with one or two short alleles for AVPR1a rs1, but not for individuals with only long alleles. Oxytocin, vasopressin, and their receptor genes may significantly influence prosocial behavior and may lie at the core of the caregiving behavioral system.