Protecting and reactivating memories

I want to point to two recent Science Magazine articles on memory. From the magazine's summaries..

Protecting memories from stress

It is widely accepted that stress has a negative impact on memory retrieval. But specific approaches to learning can counteract this effect. Smith et al. found that when memory was tested immediately after the onset of stress, stress effects were reduced. Furthermore, when subjects learned novel material by using a highly effective learning technique involving practice tests, their memory was also protected against the negative effects of stress.

Smith et al. Abstract:

More than a decade of research has supported a robust consensus: Acute stress impairs memory retrieval. We aimed to determine whether a highly effective learning technique could strengthen memory against the negative effects of stress. To bolster memory, we used retrieval practice, or the act of taking practice tests. Participants first learned stimuli by either restudying or engaging in retrieval practice. Twenty-four hours later, we induced stress in half of the participants and assessed subsequent memory performance. Participants who learned by restudying demonstrated the typical stress-related memory impairment, whereas those who learned by retrieval practice were immune to the deleterious effects of stress. These results suggest that the effects of stress on memory retrieval may be contingent on the strength of the memory representations themselves.

How to reactivate forgotten memories

Sophisticated techniques can decode stimulus representations for items held in a person's working memory. However, when subjects shift their attention toward something else, the neural representation of the now unattended item drops to baseline, as though the item has been forgotten. Rose et al. used single-pulse transcranial magnetic stimulation (TMS) to briefly reactivate the representation of an unattended item. A short pulse of TMS enhanced recognition of “forgotten” stimuli, bringing an unattended item back into focal attention.

Rose et al. Abstract:

The ability to hold information in working memory is fundamental for cognition. Contrary to the long-standing view that working memory depends on sustained, elevated activity, we present evidence suggesting that humans can hold information in working memory via “activity-silent” synaptic mechanisms. Using multivariate pattern analyses to decode brain activity patterns, we found that the active representation of an item in working memory drops to baseline when attention shifts away. A targeted pulse of transcranial magnetic stimulation produced a brief reemergence of the item in concurrently measured brain activity. This reactivation effect occurred and influenced memory performance only when the item was potentially relevant later in the trial, which suggests that the representation is dynamic and modifiable via cognitive control. The results support a synaptic theory of working memory.

Reversing the effect of booze on the brain.

Assuming that data on female rats can be extrapolated to humans, a bit of work that makes me feel better about my daily habits of aerobic swimming and a robust happy hour...Maynard and Leasure show that loss of nerve cells caused by binge drinking can be reversed by exercise, which acts to promote natural self-repair processes.:

Binge drinking damages the brain, and although a significant amount of recovery occurs with abstinence, there is a need for effective strategies to maximize neurorestoration. In contrast to binge drinking, exercise promotes brain health, so the present study assessed whether it could counteract ethanol-induced damage by augmenting natural self-repair processes following one or more binge exposures. Adult female rats were exposed to 0 (control), 1 or 2 binges, using an established 4-day model of binge-induced neurodegeneration. Half of the animals in each group remained sedentary, or had running wheel access beginning 7 days after the final binge, and were sacrificed 28 days later. To assess binge-induced hippocampal damage and exercise restoration, we quantified volume of the dentate gyrus and number of granule neurons. We found that a single binge exposure significantly decreased the volume of the dentate gyrus and number of granule neurons. A second binge did not exacerbate the damage. Exercise completely restored baseline volume and granule neuron numbers. To investigate a potential mechanism of this restoration, we administered IdU (a thymidine analog) in order to label cells generated after the first binge. Previous studies have shown that neurogenesis in the dentate gyrus is decreased by binge alcohol exposure, and that the hippocampus responds to this insult by increasing cell genesis during abstinence. We found increased IdU labeling in binge-exposed animals, and a further increase in binged animals that exercised. Our results indicate that exercise reverses long-lasting hippocampal damage by augmenting natural self-repair processes.

The brain adapts to dishonesty.

From Garrett et al., some information on neural correlates of what might be going on in Donald Trump's brain....

Dishonesty is an integral part of our social world, influencing domains ranging from finance and politics to personal relationships. Anecdotally, digressions from a moral code are often described as a series of small breaches that grow over time. Here we provide empirical evidence for a gradual escalation of self-serving dishonesty and reveal a neural mechanism supporting it. Behaviorally, we show that the extent to which participants engage in self-serving dishonesty increases with repetition. Using functional MRI, we show that signal reduction in the amygdala is sensitive to the history of dishonest behavior, consistent with adaptation. Critically, the extent of reduced amygdala sensitivity to dishonesty on a present decision relative to the previous one predicts the magnitude of escalation of self-serving dishonesty on the next decision. The findings uncover a biological mechanism that supports a 'slippery slope': what begins as small acts of dishonesty can escalate into larger transgressions.

Genetic variants linked to education predict longevity

I'll follow yesterday's post on genetic variation and societal outcomes by passing on yet another piece, this one from Marioni et al.:

Significance

Individuals with more education tend to live longer. Genetic variants have been discovered that predict educational attainment. We tested whether a “polygenic score” based on these genetic variants could make predictions about people’s lifespan. We used data from three cohort studies (including >130,000 participants) to examine the link between offspring polygenic score for education and parental longevity. Across the studies, we found that participants with more education-linked genetic variants had longer-living parents; compared with those with the lowest genetic education scores, those with the highest scores had parents who lived on average 6 months longer. This finding suggests the hypothesis that part of the ultimate explanation for the extended longevity of better-educated people is an underlying, quantifiable, genetic propensity.

Abstract

Educational attainment is associated with many health outcomes, including longevity. It is also known to be substantially heritable. Here, we used data from three large genetic epidemiology cohort studies (Generation Scotland, n = ∼17,000; UK Biobank, n = ∼115,000; and the Estonian Biobank, n = ∼6,000) to test whether education-linked genetic variants can predict lifespan length. We did so by using cohort members’ polygenic profile score for education to predict their parents’ longevity. Across the three cohorts, meta-analysis showed that a 1 SD higher polygenic education score was associated with ∼2.7% lower mortality risk for both mothers (total ndeaths = 79,702) and ∼2.4% lower risk for fathers (total ndeaths = 97,630). On average, the parents of offspring in the upper third of the polygenic score distribution lived 0.55 y longer compared with those of offspring in the lower third. Overall, these results indicate that the genetic contributions to educational attainment are useful in the prediction of human longevity.

Genetic correlates of social deprivation and household income

From Hill et al.:

 Highlights

•Common SNPs (single nucleotide polymorphisms) explain 21% of social deprivation and 11% of household income 

•Two loci attained genome-wide significance for household income 

•Genes in these loci have been linked to synaptic plasticity 

•Genetic correlations were found between both measures of SES and many other traits

Summary

Individuals with lower socio-economic status (SES) are at increased risk of physical and mental illnesses and tend to die at an earlier age. Explanations for the association between SES and health typically focus on factors that are environmental in origin. However, common SNPs have been found collectively to explain around 18% of the phenotypic variance of an area-based social deprivation measure of SES. Molecular genetic studies have also shown that common physical and psychiatric diseases are partly heritable. It is possible that phenotypic associations between SES and health arise partly due to a shared genetic etiology. We conducted a genome-wide association study (GWAS) on social deprivation and on household income using 112,151 participants of UK Biobank. We find that common SNPs explain 21% of the variation in social deprivation and 11% of household income. Two independent loci attained genome-wide significance for household income, with the most significant SNP in each of these loci being rs187848990 on chromosome 2 and rs8100891 on chromosome 19. Genes in the regions of these SNPs have been associated with intellectual disabilities, schizophrenia, and synaptic plasticity. Extensive genetic correlations were found between both measures of SES and illnesses, anthropometric variables, psychiatric disorders, and cognitive ability. These findings suggest that some SNPs associated with SES are involved in the brain and central nervous system. The genetic associations with SES obviously do not reflect direct causal effects and are probably mediated via other partly heritable variables, including cognitive ability, personality, and health.

More exercise, less depression.

Reynolds points to a number of interesting meta-analyses that pool outcomes from past research involving more than a million men and women to show that regular exercise makes us more resistant to depression. Schuch et al. find:

...men and women with the lowest fitness were about 75 percent more likely to have been given diagnoses of depression than the people with the greatest fitness. The men and women in the middle third were almost 25 percent more likely to develop depression than those who were the most fit.

Some of the same authors pooled results from 25 studies that evaluated exercise as a treatment for depression:

...pooled results persuasively showed that exercise, especially if it is moderately strenuous, such as brisk walking or jogging, and supervised, so that people complete the entire program, has a “large and significant effect” against depression

And, on mechanisms, a clip from another Schuch et al. piece combining the results of twenty studies involving 1353 people to evaluate the neurobiological effects of exercise among people with major depressive disorder (MDD)...

The results demonstrate that a single bout of exercise increases atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), copepetin and growth hormone among people with MDD. Exercise also potentially promotes long-term adaptations of copeptin, thiobarbituric acid reactive species (TBARS) and total mean frequency (TMF). However, there is limited evidence that exercise promotes adaptations on neurogenesis, inflammation biomarkers and brain structure. Associations between depressive symptoms improvement and hippocampus volume and IL-1β were found. Nevertheless, the paucity of studies and limitations presented within, precludes a more definitive conclusion of the underlying neurobiological explanation for the antidepressant effect of exercise in people with MDD.

Networks of conforming or nonconforming individuals always reach a satisfactory state

Here is an intriguing study from Ramazi et al., who use linear-threshold-based dynamic models to show that whether individuals go with or against the crowd, a stable and satisfactory outcome results. (The model code, given in the text of the article, I don't even begin to understand...so I take their word for the results.)

Binary decisions of agents coupled in networks can often be classified into two types: “coordination,” where an agent takes an action if enough neighbors are using that action, as in the spread of social norms, innovations, and viral epidemics, and “anticoordination,” where too many neighbors taking a particular action causes an agent to take the opposite action, as in traffic congestion, crowd dispersion, and division of labor. Both of these cases can be modeled using linear-threshold–based dynamics, and a fundamental question is whether the individuals in such networks are likely to reach decisions with which they are satisfied. We show that, in the coordination case, and perhaps more surprisingly, also in the anticoordination case, the agents will indeed always tend to reach satisfactory decisions, that is, the network will almost surely reach an equilibrium state. This holds for every network topology and every distribution of thresholds, for both asynchronous and partially synchronous decision-making updates. These results reveal that irregular network topology, population heterogeneity, and partial synchrony are not sufficient to cause cycles or nonconvergence in linear-threshold dynamics; rather, other factors such as imitation or the coexistence of coordinating and anticoordinating agents must play a role.

Online social interaction associated with reduced mortality risk.

Hobbs et al. apply longitudinal statistical models to two massive databases to show that online social interactions, just like old-fashioned networks in the offline world, correlate with increased longevity:

Social interactions increasingly take place online. Friendships and other offline social ties have been repeatedly associated with human longevity, but online interactions might have different properties. Here, we reference 12 million social media profiles [of Facebook users] against California Department of Public Health vital records and use longitudinal statistical models to assess whether social media use is associated with longer life. The results show that receiving requests to connect as friends online is associated with reduced mortality but initiating friendships is not. Additionally, online behaviors that indicate face-to-face social activity (like posting photos) are associated with reduced mortality, but online-only behaviors (like sending messages) have a nonlinear relationship, where moderate use is associated with the lowest mortality. These results suggest that online social integration is linked to lower risk for a wide variety of critical health problems. Although this is an associational study, it may be an important step in understanding how, on a global scale, online social networks might be adapted to improve modern populations’ social and physical health.

Stock trading - gut feelings help with risky decisions.

I've done a number of posts describing studies trying to determine what characteristics might distinguish successful stock traders (enter 'traders' in the MindBlog search box.) Here is a further offering in this vein from Kandasamy et al. correlating interoceptive ability with survival on a London trading floor:

Interoception is the sensing of physiological signals originating inside the body, such as hunger, pain and heart rate. People with greater sensitivity to interoceptive signals, as measured by, for example, tests of heart beat detection, perform better in laboratory studies of risky decision-making. However, there has been little field work to determine if interoceptive sensitivity contributes to success in real-world, high-stakes risk taking. Here, we report on a study in which we quantified heartbeat detection skills in a group of financial traders working on a London trading floor. We found that traders are better able to perceive their own heartbeats than matched controls from the non-trading population. Moreover, the interoceptive ability of traders predicted their relative profitability, and strikingly, how long they survived in the financial markets. Our results suggest that signals from the body - the gut feelings of financial lore - contribute to success in the markets.

The teenage brain and the pleasure of “likes”

Rabin points to work by Sherman et al. showing that positive feedback given to a teenager's post on social media ('likes') stimulates the same reward center in the brain activated by thoughts of sex, money or ice cream...

We investigated a unique way in which adolescent peer influence occurs on social media. We developed a novel functional MRI (fMRI) paradigm to simulate Instagram, a popular social photo-sharing tool, and measured adolescents' behavioral and neural responses to likes, a quantifiable form of social endorsement and potential source of peer influence. Adolescents underwent fMRI while viewing photos ostensibly submitted to Instagram. They were more likely to like photos depicted with many likes than photos with few likes; this finding showed the influence of virtual peer endorsement and held for both neutral photos and photos of risky behaviors (e.g., drinking, smoking). Viewing photos with many (compared with few) likes was associated with greater activity in neural regions implicated in reward processing, social cognition, imitation, and attention. Furthermore, when adolescents viewed risky photos (as opposed to neutral photos), activation in the cognitive-control network decreased. These findings highlight possible mechanisms underlying peer influence during adolescence.

Social media's globe-shaking power.

Like many of you, I am more than completely overwhelmed by recent political events and the avalanche of thoughtful commentary on them. I am one of a group of retired guys here in Fort Lauderdale whose members have been spamming each other with interesting articles we find. I am particularly struck by a piece from NYTimes columnist Farhad Manjoo on how the world I assumed I was living in has been shattered. Below are some edited and rearranged clips.

Starting with the recent election...

...widespread misinformation spread online was a primary factor in the race’s outcome...On Monday, both Google and Facebook altered their advertising policies to explicitly prohibit sites that traffic in fake news from making money off lies. That’s very likely a worthwhile fix, even if it comes too late. The internet has loosened our collective grasp on the truth...the dangers posed by fake news are just a symptom of a deeper truth... social media (such as Facebook, WhatsApp, WeChat, Instagram, Twitter, Weibo, etc.) has become an increasingly powerful cultural and political force, to the point that its effects are now beginning to alter the course of global events.

The election of Donald J. Trump is perhaps the starkest illustration yet that across the planet, social networks are helping to fundamentally rewire human society. They have subsumed and gutted mainstream media. They have undone traditional political advantages like fund-raising and access to advertising. And they are destabilizing and replacing old-line institutions and established ways of doing things, including political parties, transnational organizations and longstanding, unspoken social prohibitions against blatant expressions of racism and xenophobia...by putting out a message that resonated with people online, Mr. Trump hacked through every established political order...Most important, because these services allow people to communicate with one another more freely, they are helping to create surprisingly influential social organizations among once-marginalized groups.

There has been a

...shifting of the "Overton Window,” a term coined by the researcher Joseph P. Overton to describe the range of subjects that the mainstream media deems publicly acceptable to discuss...From about the early 1980s until the very recent past, it was usually considered unwise for politicians to court views deemed by most of society to be out of the mainstream, things like overt calls to racial bias (there were exceptions, of course, like the Willie Horton ad). But the internet shifted that window...now each person with once-maligned views can see that he’s not alone. And when these people find one another, they can do things — create memes, publications and entire online worlds that bolster their worldview, and then break into the mainstream. The groups also become ready targets for political figures like Mr. Trump, who recognize their energy and enthusiasm and tap into it for real-world victories...the Overton Window isn’t just shifting on the right. We see it happening on the left, too. Mr. Sanders campaigned on an anti-Wall Street platform that would have been unthinkable for a Democrat just a decade ago.

Mr. Trump is just the tip of the iceberg. Prepare for interesting times.

Sex differences in brain regulation of aggression

Interesting work from Terranova et al., done with hamsters, and almost certainly applicable to us humans. Here is their summary of the significance of the study, and the abstract with more technical stuff:

Significance

There are profound sex differences in the expression of social behavior and in the incidence of many psychiatric disorders, and yet little is known about how the brain mechanisms underlying these phenomena differ in females and males. Here, we report that serotonin (5-HT) and arginine–vasopressin (AVP) act in opposite ways within the hypothalamus to regulate dominance and aggression in females and males. Dominance and aggression are promoted by 5-HT in females and by AVP in males. Because dominance and aggressiveness have been linked to the resistance to stress-related psychiatric disorders, these disorders may be more effectively treated with 5-HT–targeted drugs in females and AVP-targeted drugs in males.

Abstract

There are profound sex differences in the incidence of many psychiatric disorders. Although these disorders are frequently linked to social stress and to deficits in social engagement, little is known about sex differences in the neural mechanisms that underlie these phenomena. Phenotypes characterized by dominance, competitive aggression, and active coping strategies appear to be more resilient to psychiatric disorders such as posttraumatic stress disorder (PTSD) compared with those characterized by subordinate status and the lack of aggressiveness. Here, we report that serotonin (5-HT) and arginine–vasopressin (AVP) act in opposite ways in the hypothalamus to regulate dominance and aggression in females and males. Hypothalamic injection of a 5-HT1a agonist stimulated aggression in female hamsters and inhibited aggression in males, whereas injection of AVP inhibited aggression in females and stimulated aggression in males. Striking sex differences were also identified in the neural mechanisms regulating dominance. Acquisition of dominance was associated with activation of 5-HT neurons within the dorsal raphe in females and activation of hypothalamic AVP neurons in males. These data strongly indicate that there are fundamental sex differences in the neural regulation of dominance and aggression. Further, because systemically administered fluoxetine increased aggression in females and substantially reduced aggression in males, there may be substantial gender differences in the clinical efficacy of commonly prescribed 5-HT–active drugs such as selective 5-HT reuptake inhibitors. These data suggest that the treatment of psychiatric disorders such as PTSD may be more effective with the use of 5-HT–targeted drugs in females and AVP-targeted drugs in males.

Are your emotions 'Black and White' or 'Shades of Gray'? - Brain correlates.

Satpute et al. show that how we think about emotion shapes our perception and neural representation of emotion. They asked subjects to judge emotional expressions as fearful or calm using either categorical terms or a continuous scale. They found that categorical-thinking-induced shifts in emotion perception toward “fear” or toward “calm” were associated with corresponding shifts in neural activity.:

The demands of social life often require categorically judging whether someone’s continuously varying facial movements express “calm” or “fear,” or whether one’s fluctuating internal states mean one feels “good” or “bad.” In two studies, we asked whether this kind of categorical, “black and white,” thinking can shape the perception and neural representation of emotion. Using psychometric and neuroimaging methods, we found that (a) across participants, judging emotions using a categorical, “black and white” scale relative to judging emotions using a continuous, “shades of gray,” scale shifted subjective emotion perception thresholds; (b) these shifts corresponded with activity in brain regions previously associated with affective responding (i.e., the amygdala and ventral anterior insula); and (c) connectivity of these regions with the medial prefrontal cortex correlated with the magnitude of categorization-related shifts. These findings suggest that categorical thinking about emotions may actively shape the perception and neural representation of the emotions in question.

Thoughts about Dying in America.

Pizzo offers a summary of a recent Institute of Medicine report, with the title "Thoughts about Dying in America: Enhancing the impact of one’s life journey and legacy by also planning for the end of life."

This Perspective offers a summary of the recommendations in the Institute of Medicine report Dying in America. How we die is a deeply personal issue that each of us will face. However, the approach to end-of-life (EOL) care in the United States needs improvement. Too frequently, healthcare delivery is uncoordinated and has many providers who are not adequately prepared to have meaningful conversations about EOL planning. This is amplified by payment systems and policies that create impediments, misunderstanding, and sometimes misinformation. Dying in America made five recommendations to improve quality and honor individual preferences near the EOL beginning with making conversations with providers and families something that occurs during various phases of the life cycle and not just when one is facing serious illness or possible EOL. It was recommended (i) that public and private payers and care delivery organizations cover the provision of comprehensive care that is accessible and available to individuals on a 24/7 schedule; (ii) that professional societies and other entities establish standards for clinician patient communication and advance care planning and that payers and care delivery organizations adopt them; (iii) that educational institutions, credentialing bodies, accrediting boards, state regulatory agencies, and care delivery organizations establish palliative care training, certification, and/or licensure requirements; (iv) that public and private payers and care delivery organizations integrate the financing of health and social services; and (v) that public and private organizations should engage their constituents and provide fact-based information to encourage advance care planning and informed choice.

Our working memory modulates our conscious access to suppressed threatening information.

Our processing of emotional information is susceptible to working memory (WM) modulations - emotional faces trigger much stronger responses in the fronto-thalamic occipital network when they match an emotional word held in WM than when they do not. Liu et al. show that WM tasks can also influence the nonconscious processing of emotional signals. Their explanation of the procedure used:

We used a modified version of the delayed-match-to-sample paradigm. Specifically, participants were instructed to keep a face (either fearful or neutral) in WM while performing a target-detection task. The target, another face with a new identity (fearful or neutral), was suppressed from awareness utilizing continuous flash suppression. In this technique, the target is monocularly presented and hidden from visual awareness by simultaneously presenting dynamic noise to the other eye. We measured the time it took for the suppressed face to emerge from suppression. We specifically tested whether faces would emerge from suppression more quickly if they matched the emotional valence of WM contents than if they did not.

Here is their abstract:

Previous research has demonstrated that emotional information processing can be modulated by what is being held in working memory (WM). Here, we showed that such content-based WM effects can occur even when the emotional information is suppressed from conscious awareness. Using the delayed-match-to-sample paradigm in conjunction with continuous flash suppression, we found that suppressed threatening (fearful and angry) faces emerged from suppression faster when they matched the emotional valence of WM contents than when they did not. This effect cannot be explained by perceptual priming, as it disappeared when the faces were only passively viewed and not held in WM. Crucially, such an effect is highly specific to threatening faces but not to happy or neutral faces. Our findings together suggest that WM can modulate nonconscious emotion processing, which highlights the functional association between nonconsciously triggered emotional processes and conscious emotion representation.

View a flickering stimulus before you try to read fine print…

A nice piece of work from Arnold et al.:

Significance

Distinct anatomical visual pathways can be traced through the human central nervous system. These have been linked to specialized functions, such as encoding information about spatial forms (like the human face and text) and stimulus dynamics (flicker or movement). Our experiments are inconsistent with this strict division. They show that mechanisms responsive to flicker can alter form perception, with vision transiently sharpened by weakening the influence of flicker-sensitive mechanisms by prolonged exposure to flicker. So, next time you are trying to read fine print, you might be well advised to first view a flickering stimulus!

Abstract

Human vision is surprisingly malleable. A static stimulus can seem to move after prolonged exposure to movement (the motion aftereffect), and exposure to tilted lines can make vertical lines seem oppositely tilted (the tilt aftereffect). The paradigm used to induce such distortions (adaptation) can provide powerful insights into the computations underlying human visual experience. Previously spatial form and stimulus dynamics were thought to be encoded independently, but here we show that adaptation to stimulus dynamics can sharpen form perception. We find that fast flicker adaptation (FFAd) shifts the tuning of face perception to higher spatial frequencies, enhances the acuity of spatial vision—allowing people to localize inputs with greater precision and to read finer scaled text, and it selectively reduces sensitivity to coarse-scale form signals. These findings are consistent with two interrelated influences: FFAd reduces the responsiveness of magnocellular neurons (which are important for encoding dynamics, but can have poor spatial resolution), and magnocellular responses contribute coarse spatial scale information when the visual system synthesizes form signals. Consequently, when magnocellular responses are mitigated via FFAd, human form perception is transiently sharpened because “blur” signals are mitigated.

Why do people in big cities move faster?

A number of studies have shown that people in big cities move faster. Why is this? Pontzer describes work by Ahmed et al. suggesting that our brains use metabolic energy cost to determine the speed with which we (and other animals) move towards a reward.

For many tasks, such as walking, the metabolic energy (i.e., calories) expended per distance traveled is a function of speed; moving faster requires more energy per meter. A reward’s value can be a function of speed as well. Under a temporal discounting model, a reward’s value decreases the longer it takes to obtain it; food might decay or be lost to competitors, the comfortable seats on the rush-hour train might be taken. Given the cost:speed function for a given task and the value:time function for a given reward, one can solve for the speed that maximizes net return for a given action.

Ahmed and colleagues tested their model in a series of reaching tasks with human subjects and found strong support for it...despite its simplicity the model makes reliable predictions across a variety of different tasks and even across species. Analyzing the behavior of finches reported in an experimental study of foraging behavior, Ahmed and colleagues showed that their model correctly predicts whether the birds chose to walk (which is slow but metabolically inexpensive) or fly (fast but costly) to acquire food. When the time to acquire the food increased, its value as estimated by the discounting model decreased, and as predicted the birds chose to walk. In a separate analysis of isometric force production in human subjects, their model correctly predicted subjects’ decreasing sensitivity to task duration as the force exerted decreased.

That the model’s predictions work well across species suggests it may reflect a common, evolved neurobiological mechanism that is shared across species. Ahmed and colleagues suggest, for example, that the neural circuits involved in generating actions should be strongly coupled to the circuits involved in deciding between actions. Such shared, evolved neurological mechanisms are powerful tools for research, as they present a common framework for comparing behavioral strategies across species, tasks, and environments.

Pontzer's final paragraph:

For my fellow New Yorkers, Ahmed and colleagues’ model suggests two, mutually compatible reasons that we habitually walk faster, and less efficiently, than our relaxed, rural comrades (see figure above). We may perceive greater rewards are at stake, and given the remarkable sums of money exchanged each day in the city, that assessment may well be accurate for some. Alternatively, with over 8 million fellow primates foraging for the same resources, we may sense that the rewards we seek are slipping away more quickly — something to ponder next time you’re running for the train.

The mathematical model developed by Ahmed et al. is a bit more complex than is appropriate for a description here, but can be found in their paper.

Social class and attentiveness to others.

More on “The rich are different from you and me.” (F. Scott Fitzgerald) “Yes, They have more money.” (Hemingway). Dietze and Knowles use eye movement measurements to show that people of higher social class are less attentive to other people and their faces. Their abstract, slightly edited:

We theorize that people’s social class affects their appraisals of others’ motivational relevance—the degree to which others are seen as potentially rewarding, threatening, or otherwise worth attending to. Supporting this account, three studies indicate that social classes differ in the amount of attention their members direct toward other human beings. In the first study, wearable technology was used to film the visual fields of pedestrians on city streets; higher-class participants looked less at other people than did lower-class participants. A second study tracked participants’ eye movements while they viewed street scenes; higher class was associated with reduced attention to people in the images. Finally a third study used a change-detection procedure to assess the degree to which human faces spontaneously attract visual attention; faces proved less effective at drawing the attention of high-class than low-class participants, which implies that class affects spontaneous relevance appraisals. The measurement and conceptualization of social class are discussed.

Explaining gender differences in anxiety.

Li et al. find that a set of oxytocin-responsive neurons in the medial prefrontal cortex (mPFC) look similar in both sexes, but in males they secrete a protein (CRHBP) that antagonizes the effect of the corticotropin-releasing hormone (CRH) associated with stress, thus causing an anti-anxiety effect with males that is not seen in females. This suggests the possibility of developing gender specific therapies for anxiety.

Highlights

•Activation of OxtrINs (oxytocin receptor interneurons) is anxiolytic in males and prosocial in females 

•OxtrINs specifically express CRHBP, an inhibitor of the stress hormone CRH 

•CRHBP blocks activation of layer 2/3 pyramidal cells by CRH only in males 

•OxtrINs in the mPFC (medial prefrontal cortex) coordinate sexually dimorphic social/emotional behaviors

Summary

The frequency of human social and emotional disorders varies significantly between males and females. We have recently reported that oxytocin receptor interneurons (OxtrINs) modulate female sociosexual behavior. Here, we show that, in male mice, OxtrINs regulate anxiety-related behaviors. We demonstrate that corticotropin-releasing-hormone-binding protein (CRHBP), an antagonist of the stress hormone CRH, is specifically expressed in OxtrINs. Production of CRHBP blocks the CRH-induced potentiation of postsynaptic layer 2/3 pyramidal cell activity of male, but not female, mice, thus producing an anxiolytic effect. Our data identify OxtrINs as critical for modulation of social and emotional behaviors in both females and males and reveal a molecular mechanism that acts on local medial prefrontal cortex (mPFC) circuits to coordinate responses to OXT and CRH. They suggest that additional studies of the impact of the OXT/OXTR and CRHBP/CRH pathways in males and females will be important in development of gender-specific therapies.

The presidential election has spawned an effusion of interesting essays - a sampling

A rich trove of Op-Ed pieces and essays has emerged during the recent presidential campaign. I’ve accumulated a list of links, thinking each article might merit an individual blog post, but the list has become overwhelming, like everything else in the campaign. Instead of letting the list entirely fade away, I thought I would pass on selected links, with a brief note on the content of each article:

Behind Our Anxiety, The Fear of Being Unneeded. An interesting collaboration between the conservative president of the American Enterprise Institute and the Dalai Lama. It's message is that our current anxiety and malaise stems not from material needs, but from the growing number of people who feel they are no longer useful, no longer needed, no longer one with their societies. What is needed is the building of a compassionate society that creates a wealth of opportunities for meaningful work in the service of others, so that everyone who is capable of contributing can do so.

Hillary Clinton’s Juggling Act. Hillary Clinton must juggle three competing interest groups: her party’s upscale pro-trade, globalist wing; its underdog minority wing; and organized labor. She is paying a price for her triple allegiance.

The Ethics of Globalism, Nationalism, and Patriotism. A thoughtful article noting a fundamental cause of the division between globalists and nationalists: their underlying theories of human nature, the “unconstrained vision” and the “constrained vision.” If you really believe that the world is “full of good people,” then why not lower the drawbridge and leave it down? But if you have a darker view of human nature and are inclined to see more threats in the world, then you’ll want to retain full control of the drawbridge, lower it selectively, and check people’s papers before you let them in. He quotes from a David Brooks essay "The way out of this debate is not to go nationalist or globalist. It’s to return to American nationalism—espoused by people like Walt Whitman—which combines an inclusive definition of who is Our Own with a fervent commitment to assimilate and Take Care of them."

The Price of Certainty. A piece, with a video, on the work of social psychologist Arie Kruglanski, and his theory of "cognitive closure." Closure is the moment that you make a decision or form a judgment. You literally close your mind to new information. If you have high need for closure, you tend to make decisions quickly and see the world in black and white. If you have a low need for closure, you tolerate ambiguity, but often have difficulty making decisions. All of us fall naturally somewhere on this spectrum...But during times of fear and anxiety — like, for example, right now — everybody’s need for closure increases. We tend to make judgments more quickly, regardless of the facts. We’re also drawn to leaders who are decisive and paint solutions in simple terms.

The Case Against Democracy. An interesting essay Caleb Crain in The New Yorker on the history of the idea of “epistocracy,” meaning “government by the knowledgeable.”