Calculate your endurance

I thought I would pass on this fascinating item from the Random Samples section of the Oct. 29th issue of Science Magazine.  Now you can calculate exactly what carbohydrate loading you need to run a marathon in a desired amount of time:

Just about all serious marathon runners have experienced it. In the last half of a marathon, usually at about mile 21, their energy suddenly plummets. Their legs slow down, and it's almost impossible to make them go faster. Nutritionists blame carbohydrate loss: When the supply runs out, runners "hit the wall."

Now a model published this month in PLoS Computational Biology tells runners when they'll hit the wall, helping them to plan their carb-loading or refueling strategies accordingly. Benjamin Rapoport, a dual M.D.-Ph.D. student at Harvard Medical School and the Massachusetts Institute of Technology, says the idea began 5 years ago, when a class conflicted with his running in the Boston Marathon. His professor let him skip, provided he give a talk on the physiology of endurance running afterward. The talk became an annual tradition, and now he's quantified his ideas.

Rapoport's model looks at multiple factors, such as a runner's desired pace, muscle mass, and aerobic capacity, the amount of oxygen the body can deliver to its muscles. "It's a real tour de force," says physiologist Michael Joyner of the Mayo Clinic in Rochester, Minnesota, although he adds it is hard to account for all individual differences.

Which is better, chowing down days before or grabbing some sugar during the race? "Both," says sports nutritionist Edward Coyle of the University of Texas, Austin. "The carb loading will raise the glycogen levels in your muscles, and taking in carbs during the race will keep your blood glucose levels up." And now Rapoport even has an app for that: Athletes will can calculate their thresholds at http://endurancecalculator.com/.

Our minds extend beyond our heads.

I've always liked the idea, lucidly presented by Andy Clark over many years, that our minds are impossible to distinguish from our environment, because they really can't exist in the absence of a cognitive coupling between the two. I am relaying below the entire text of an instructive and interesting book review by Erik Myin of a book of commentaries on an influential 1998 paper by Andy Clark and David Chalmers titled "The extended mind." (very much worth reading, PDF here).

Where is the mind? "In the head" or "in the brain," most people might respond. The philosopher Gilbert Ryle gave a different answer:

The statement "the mind is in its own place," as theorists might construe it, is not true, for the mind is not even a metaphorical "place." On the contrary, the chessboard, the platform, the scholar's desk, the judge's bench, the lorry, the driver's seat, the studio and the football field are among its places. (1)

Recently, this idea of the mind not being confined to the head has been reinvigorated by philosophers and cognitive scientists, who see the mind as "spreading out" or "extending" into the world. "How do you know the way to San José?" philosopher John Haugeland has famously asked (2). Chances are you don't have some inner analog of a printed map. Rather, you know where you should enter the highway, and then you get there by following the road signs. Your knowledge seems to be partially "implemented" in the environment. There is now a blooming field of research into "situation cognition," which explores how cognitive or mental phenomena such as problem solving or remembering can be strongly dependent on interactions between subjects and their environments.

The possible far-reaching implications of a situated view of cognition were brought into sharp focus by Andy Clark and David Chalmers in their 1998 paper "The extended mind" (3). There they defend the idea that the mind "extends" into the environment in cases in which a human organism and the environment become cognitively coupled systems. Their by now iconic illustration of cognitive coupling involves "Otto," a "slightly amnesic" person, who uses a notebook to write down important facts that he is otherwise likely to forget. Unlike a person who remembers the address of the Museum of Modern Art by relying on natural memory, Otto recalls it by accessing his notebook. If one supposes that the notebook is constantly available to Otto and that what is written in it is endorsed by Otto, it becomes plausible—so Clark and Chalmers argue—that Otto's memory extends to include the notebook. After all, they notice, Otto's notes seem to play exactly the same role as memory traces in other people. Wouldn't it be chauvinistic to restrict the mind's extent to what's natural and inner?

Clark and Chalmers's paper has triggered a vigorous and continuing debate. Nonbelievers concede that numerous tight causal couplings between minds and environments exist, but they deny that it therefore makes sense to speak of an extended mind instead of a mind in a person that closely interacts with an environment. All things considered, they argue, thoughts remain in persons—never in objects like notebooks, however closely dependent a person could become on them.

Enthusiasts for the extended mind thesis insist that a close causal coupling between persons and environments can license the conclusion that the mind spreads into the environment. Some follow the argument in Clark and Chalmers that infers extendedness from the fact that external elements can play a role that would be considered as cognitive if played by something internal to a person.

Other supporters of the idea are suspicious of this argument from parity. They note that the most interesting cases of causal coupling are those in which the environment does not simply function as some ersatz internal milieu—when the involvement of external means makes possible forms of cognition that were not possible without them. For example, when pen and paper, symbolic systems, or computers make possible calculations, computations, and, ultimately, scientific theories. Those taking this position hold that it is when the environment becomes a necessary factor in enabling novel cognitive processes that the mind extends.

In The Extended Mind, philosopher Richard Menary (University of Wollongong) brings together the Clark and Chalmers paper and several responses to it. The collection, lucidly introduced by Menary, will neither definitively prove nor deal the deathblow to the idea that "the place of the mind" is the world—nor even establish that there really is such a question about "the place of the mind" that needs to be answered. Rather, the volume provides carefully drawn arguments for and against different interpretations of the extended mind thesis, often with extensive reference to empirical material. Several of the papers in the collection are excellent.

To take one fascinating idea, consider Susan Hurley on "variable neural correlates." We are comfortable with the correlation between types of experience and types of brain states, and undoubtedly such variation is one important source for the idea that the mind is in the head. Hurley notes, however, that there is also a dependence of experience on type of interaction with the environment, one not aligned to strictly neural properties. For example, when blind people haptically read Braille text, activity in the visual cortex seems to correlate with tactile experience. In people who are not blind, tactile experience correlates with activity in the tactile cortex. What explains the common enabling of tactile experience by the different kinds of cortex seems to be tactile causal coupling with the environment, rather than strictly neural type. According to Hurley, and others, the same kind of correlation-tracking reasoning that convinces us, in standard cases, that the mind is in the brain should here lead to the conclusion that the mind is not in the head.

References

* 1. G. Ryle, The Concept of Mind (Hutchinson, London, 1949).
* 2. J. Haugeland, Having Thought: Essays in the Metaphysics of Mind (Harvard Univ. Press, Cambridge, MA, 1998).
* 3. A. Clark, D. J. Chalmers, Analysis 58, 7 (1998).

Light at night makes us fat.

...at least that is what experiments on mice done by Fonken et al. suggest.  The experiments were motivated by wondering whether the global increase in obesity that is occurring might be related to the extended night time light exposure that goes with our modern life style and is known to disrupt the biological clocks that regulate our energy metabolism.  Their abstract is worth reading:

The global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night (LAN) and shift work. Circadian regulation of energy homeostasis is controlled by an endogenous biological clock that is synchronized by light information. To promote optimal adaptive functioning, the circadian clock prepares individuals for predictable events such as food availability and sleep, and disruption of clock function causes circadian and metabolic disturbances. To determine whether a causal relationship exists between nighttime light exposure and obesity, we examined the effects of LAN on body mass in male mice. Mice housed in either bright (LL) or dim (DM) LAN have significantly increased body mass and reduced glucose tolerance compared with mice in a standard (LD) light/dark cycle, despite equivalent levels of caloric intake and total daily activity output. Furthermore, the timing of food consumption by DM and LL mice differs from that in LD mice. Nocturnal rodents typically eat substantially more food at night; however, DM mice consume 55.5% of their food during the light phase, as compared with 36.5% in LD mice. Restricting food consumption to the active phase in DM mice prevents body mass gain. These results suggest that low levels of light at night disrupt the timing of food intake and other metabolic signals, leading to excess weight gain. These data are relevant to the coincidence between increasing use of light at night and obesity in humans.

Oxytocin selectively improves social cognition.

Numerous studies on pro-social effect of oxytocin have generated interest in oxytocin’s potential to ameliorate social deficits in such disorders as social phobias and autism. Bartz et al suggest that oxytocin might increase the salience of social cues by altering specific motivational or cognitive states. If this is the case, the effects of oxytocin might be most pronounced in individuals who, at baseline, are less socially proficient. They examined a group of 27 healthy men (average age of 27), using a randomized, double-blind, placebo-controlled, crossover challenge in which participants received either intranasal oxytocin or a placebo and performed an empathic-accuracy task that naturalistically measures social-cognitive abilities. They also measured variance in baseline social competencies with the Autism Spectrum Quotient (AQ), a self-report instrument developed by Baron-Cohen and others that predicts social-cognitive performance.

They found that normal variance in baseline social-cognitive competence moderates the effects of oxytocin; specifically, oxytocin improved empathic accuracy only for less socially proficient individuals. These findings constitute evidence against the popular view that oxytocin acts as a universal prosocial enhancer that can render all people social-cognitive experts. Instead, oxytocin appears to play a more nuanced role in social cognition, and helps only some people.

Here is a figure of their data:

Figure - Results of the regression analysis: predicted empathic accuracy as a function of Autism Spectrum Quotient (AQ) raw score for the oxytocin condition (dashed line) and placebo condition (solid line). The dotted curves indicate 95% confidence intervals (CIs). Lower numbers on the AQ reflect greater social-cognitive proficiency. Higher numbers on the empathic-accuracy index reflect superior performance. Predicted values are shown only for observed levels of the AQ; the predictive equation is as follows: empathic accuracy = 0.44 + 0.048(drug condition) – 0.018(AQ) + 0.018(Drug Condition × AQ).

de Waal on the Biology of Morality

A colleague pointed out this thoughtful piece on morals without God written by primatologist Frans de Waal.

The debate is less about the truth than about how to handle it. For those who believe that morality comes straight from God the creator, acceptance of evolution would open a moral abyss...but I am wary of anyone whose belief system is the only thing standing between them and repulsive behavior. Why not assume that our humanity, including the self-control needed for livable societies, is built into us? Does anyone truly believe that our ancestors lacked social norms before they had religion? Did they never assist others in need, or complain about an unfair deal? Humans must have worried about the functioning of their communities well before the current religions arose, which is only a few thousand years ago. Not that religion is irrelevant...but it is an add-on rather than the wellspring of morality.

de Waal gives an engaging review of his observations on primate behavior that show clear evidence for moral and altruistic behaviors that can not be linked to simple "selfish gene" models and he ends with this comment about monkey and chimpanzee behaviors:

...they strive for a certain kind of society. For example, female chimpanzees have been seen to drag reluctant males towards each other to make up after a fight, removing weapons from their hands, and high-ranking males regularly act as impartial arbiters to settle disputes in the community. I take these hints of community concern as yet another sign that the building blocks of morality are older than humanity, and that we do not need God to explain how we got where we are today. On the other hand, what would happen if we were able to excise religion from society? I doubt that science and the naturalistic worldview could fill the void and become an inspiration for the good. Any framework we develop to advocate a certain moral outlook is bound to produce its own list of principles, its own prophets, and attract its own devoted followers, so that it will soon look like any old religion.

How rummination can both help and hinder.

Altamirano et al. do a simple study that shows that depressive rumminators (like myself?) are more stable in maintaining goals, but sacrifice flexibility:

Although previous research suggests that depressive ruminators tend to become stuck in a particular mind-set, this mental inflexibility may not always be disadvantageous; in some cases, it may facilitate active maintenance of a single task goal in the face of distraction. To evaluate this hypothesis, we tested 98 college students, who differed in ruminative tendencies and dysphoria levels, on two executive-control tasks. One task emphasized fast-paced shifting between goals (letter naming), and one emphasized active goal maintenance (modified Stroop). Higher ruminative tendencies predicted more errors on the goal-shifting task but fewer errors on the goal-maintenance task; these results demonstrated that ruminative tendencies have both detrimental and beneficial effects. Moreover, although ruminative tendencies and dysphoria levels were moderately correlated (r = .42), higher dysphoria levels predicted more errors on the goal-maintenance task; this finding indicates that rumination and dysphoria can have opposing effects on executive control. Overall, these results suggest that depressive rumination reflects a trait associated with more stability (goal maintenance) than flexibility (goal shifting).

MindBlog is on the road.

Tuesday evening... little do they realize  (my two Abyssinian cats, Marvin and Melvin) that they will be on the road at 7 a.m. tomorrow morning heading south from Madison WI to MindBlog's winter home in Fort Lauderdale , FL, where I spend the next five winter months.  They enjoy the car ride, looking out the car windows at adjacent drivers.  There are a few posts in the queue, but it may be largely an off week while I settle into the winter warmth of Florida.  Today we are having wind gusts up to 60 mph from a storm across the midwest, and the wind chill tomorrow is supposed to be 10 degrees.

Why that nearby cell phone conversation bothers you...

While I am reading my morning newspaper in a restaurant at breakfast, nothing ticks me off more than a nearby cell phone conversation, but I'm not bothered by two people chatting nearby. Observation of Emberson et al. suggest why this might be the case:

Why are people more irritated by nearby cell-phone conversations than by conversations between two people who are physically present? Overhearing someone on a cell phone means hearing only half of a conversation—a “halfalogue.” We show that merely overhearing a halfalogue results in decreased performance on cognitive tasks designed to reflect the attentional demands of daily activities. By contrast, overhearing both sides of a cell-phone conversation or a monologue does not result in decreased performance. This may be because the content of a halfalogue is less predictable than both sides of a conversation. In a second experiment, we controlled for differences in acoustic factors between these types of overheard speech, establishing that it is the unpredictable informational content of halfalogues that results in distraction. Thus, we provide a cognitive explanation for why overheard cell-phone conversations are especially irritating: Less-predictable speech results in more distraction for a listener engaged in other tasks.

The quest for simplicity.

A new Apple product has been announced recently, a new MacBook Air that is the offspring of the union of a Mac computer and an iPad. In addition to multitouch, the new hardware and software incorporate the video phone software FaceTime, an App Store and other popular features of Apple’s hand-held products. Purists are bemoaning the even further dumbing down of the personal computer, while software companies like Microsoft and Adobe fear the advent of a simple click to purchase system in the App Store will weaken their grip on elaborate licensing and installation disk sales. Consumers like Apple products because they don't have to face the confusing multiple software and hardware choices that must be made to use the Microsoft or Google Android operating systems.

What we are seeing in both the consumer economy and in politics is a flight from complexity. The genius of Apple products is that their options are limited, disciplined, and presented simply.

The Tea Party, as well as religious fundamentalism, also reflect this flight from complexity, by offering a simple set of basic principles to be applied in all political and economic decisions. This seems an understandable response of brains so overwhelmed by overwhelming parallel streams of conflicting media input that they shunt aside the mental effort required discern actual facts.

The saddening aspect of this is that people faced with more input than a normal human brain wants to cope with want to be told what to do, what they think (a point made by Google's chief executive and mentioned in a previous post.) Advertisements during political campaigns that appeal to rational thought and actual facts become increasingly futile, as special interests with sophistical psychological consultants craft adds to manipulate people's most primitive fears, desires, and emotions.

A Brahms Rhapsody for monday morning...

I thought I would pass on this slightly truncated version of the Brahms Rhapsody Op. 79, No. 1 that I played for the Carnaval Music group in Madison WI last Tuesday.  Here it recorded on my Steinway B at Twin Valley in Middleton, WI.

How to make yourself more powerful...

Carney et al suggest that just a few minutes of moving your body muscles into a more open expansive posture can change your behavior and body chemistry, increasing testosterone and decreasing the stress hormone cortisol:

Humans and other animals express power through open, expansive postures, and they express powerlessness through closed, contractive postures. But can these postures actually cause power? The results of this study confirmed our prediction that posing in high-power nonverbal displays (as opposed to low-power nonverbal displays) would cause neuroendocrine and behavioral changes for both male and female participants: High-power posers experienced elevations in testosterone, decreases in cortisol, and increased feelings of power and tolerance for risk; low-power posers exhibited the opposite pattern. In short, posing in displays of power caused advantaged and adaptive psychological, physiological, and behavioral changes, and these findings suggest that embodiment extends beyond mere thinking and feeling, to physiology and subsequent behavioral choices. That a person can, by assuming two simple 1-min poses, embody power and instantly become more powerful has real-world, actionable implications.

Here are some clips from the context and data the authors provide:

In research on embodied cognition, evidence suggests that bodily movements, such as facial displays, can affect emotional states. For example, unobtrusive contraction of the “smile muscle” (i.e., the zygomaticus major) increases enjoyment, the head tilting upward induces pride, and hunched postures (as opposed to upright postures) elicit more depressed feelings. Approach-oriented behaviors, such as touching, pulling, or nodding “yes,” increase preference for objects, people, and persuasive messages…no research has tested whether expansive power poses, in comparison with contractive power poses, cause mental, physiological, and behavioral change in a manner consistent with the effects of power.

In humans and other animals, testosterone levels both reflect and reinforce dispositional and situational status and dominance; internal and external cues cause testosterone to rise, increasing dominant behaviors, and these behaviors can elevate testosterone even further…testosterone levels, by reflecting and reinforcing dominance, are closely linked to adaptive responses to challenges.

Power holders show lower basal cortisol levels and lower cortisol reactivity to stressors than powerless people do, and cortisol drops as power is achieved. Although short-term and acute cortisol elevation is part of an adaptive response to challenges large (e.g., a predator) and small (e.g., waking up), the chronically elevated cortisol levels seen in low-power individuals are associated with negative health consequences, such as impaired immune functioning, hypertension, and memory loss.

 Here are the basic results:

Salivary cortisol and testosterone levels were within a normal range of ~ 0.16 μg/dl and ~60 pg/ml both before and after participants held either two high-power or two low-power poses for 1 min each. The figure shows the changes caused by the two postures (click to enlarge). The experiment is missing what would seem to be one obvious control: measurements on subjects who were given an instruction to assume an arbitrary posture unrelated to power.

Brain correlates of whether we decide to help others.

Hein et al. find that empathy-related brain responses in the anterior insula predict costly helping of others, that distinct neural responses predict helping in-group and out-group members, and that brain responses predict behavior toward outgroup members better than self-reports:

Little is known about the neurobiological mechanisms underlying prosocial decisions and how they are modulated by social factors such as perceived group membership. The present study investigates the neural processes preceding the willingness to engage in costly helping toward ingroup and outgroup members. Soccer fans witnessed a fan of their favorite team (ingroup member) or of a rival team (outgroup member) experience pain. They were subsequently able to choose to help the other by enduring physical pain themselves to reduce the other's pain. Helping the ingroup member was best predicted by anterior insula activation when seeing him suffer and by associated self-reports of empathic concern. In contrast, not helping the outgroup member was best predicted by nucleus accumbens activation and the degree of negative evaluation of the other. We conclude that empathy-related insula activation can motivate costly helping, whereas an antagonistic signal in nucleus accumbens reduces the propensity to help.

Magic numbers

Anything Daniel Gilbert writes is worth reading, and in that spirit I pass on this Op-Ed bon-bon that asks why a full course of antibiotics usually takes seven days, with stern instructions not to terminate the pills earlier. "Why not six, eight or nine and a half? Does the number seven correspond to some biological fact about the human digestive tract or the life cycle of bacteria?" The answer of course is no....

Seven is a magic number because only it can make a week, and it was given this particular power in 321 A.D. by the Roman emperor Constantine, who officially reduced the week from eight days to seven. The problem isn’t that Constantine’s week was arbitrary — units of time are often arbitrary, which is why the Soviets adopted the five-day week before they adopted the six-day week, and the French adopted the 10-day week before they adopted the 60-day vacation.

The problem is that Constantine didn’t know a thing about bacteria, and yet modern doctors continue to honor his edict. If patients are typically told that every 24 hours (24 being the magic number that corresponds to the rotation of the earth) they should take three pills (three being the magic number that divides any time period into a beginning, middle and end) and that they should do this for seven days, they will end up taking 21 pills.

If even one of those pills is unnecessary — that is, if people who take 20 pills get just as healthy just as fast as people who take 21 — then millions of people are taking at least 5 percent more medication than they actually need. This overdose contributes not only to the punishing costs of health care, but also to the evolution of the antibiotic-resistant strains of “superbugs” that may someday decimate our species. All of which seems like a rather high price to pay for fealty to ancient Rome.

A dog's dish - half empty or half full?

We know that humans vary in their underlying temperament (negative versus positive mood), with ~50% of the variation due to genetic factors.  It turns out that dogs also show variation, with more negative underlying moods predicting the degree of their distress upon separation (Being left a home alone, with the most common separation-related behaviors being vocalising, destruction and toileting). Mendl et al. test for underlying optimism/pessimism involved placing bowls in two rooms. One bowl contained food, while another was empty. After training the dogs to understand that bowls can sometimes be empty, and sometimes full, they began to place bowls in ambiguous locations. Dogs that quickly raced to the locations were more optimistic, and in search of food. Those that did not were deemed pessimistic. The more separation anxiety a dog expressed while in isolation, the more likely the dog was to have a pessimistic reaction.

Earlier retirement, earlier memory decline.

In yet another example of "use it or loose it," Rohwedder and Willis show that the earlier people retire, the more quickly their memory and general cognitive abilities decline. They note two possible models for the cognitive decline: 1.) A "unengaged lifestyle hypothesis" that suggests that the life of a retiree may lack the cognitive stimulation of the former working environment unless deliberate offsetting actions are take. 2.) A “on-the-job” retirement effect, in which mental effort decline as the retirement age approaches (a 50-year-old worker in the United States who expects to work until 65 has a much greater incentive to continue investing in mental capacity than does a worker in Italy who expects to retire at 57.) Here is a summary graph (details are in the article) :

Cognition by Percent Not Working for Pay, 60–64 Year-Old Men and Women, Weighted

Do cell phones cause cancer?

My random browsing of the October issue of Scientific American brought me to this nice summary graphic offered by physicist Bernard Leikind of his article in Skeptic magazine Vol. 15, no. 4 (2010). Utterly basic physical principles show that cell phones (or microwave ovens) could not cause cancer, the energy content of their emitted radiations is orders of magnitude below that required to rupture chemical bonds. (click to enlarge)

What makes groups of people smart?

Woolley and collaborators have studied people working in small groups, investigating why some groups appear to be smarter than others. A given group's performance on any one task did in fact predict its performance on the others, suggesting that groups have a consistent "collective intelligence." Surprisingly, the average intelligence of the individuals in the group was not the best predictor of a group's performance. The degree to which group members were attuned to social cues and their willingness to take turns speaking were more important, as was the proportion of women in the group. Here is their abstract:

Psychologists have repeatedly shown that a single statistical factor—often called "general intelligence"—emerges from the correlations among people's performance on a wide variety of cognitive tasks. But no one has systematically examined whether a similar kind of "collective intelligence" exists for groups of people. In two studies with 699 individuals, working in groups of two to five, we find converging evidence of a general collective intelligence factor that explains a group's performance on a wide variety of tasks. This "c factor" is not strongly correlated with the average or maximum individual intelligence of group members but is correlated with the average social sensitivity of group members, the equality in distribution of conversational turn-taking, and the proportion of females in the group.

A commentary by Greg Miller notes the actual tasks used to evaluate group intelligence:

Teams worked on a variety of tasks, including brainstorming to come up with possible uses for a brick and working collaboratively on problems from a test of general intelligence called Raven's Advanced Progressive Matrices. These problems involve evaluating several shapes arranged in a grid and identifying the missing item that would complete the pattern. The groups also worked on more real-world scenarios, such as planning a shopping trip for a group of people who shared a car. The researchers scored these tests according to predetermined rules that considered several factors (awarding points when shoppers got to buy items on their list, for example). Each participant also took an abbreviated version of the Raven's test as a measure of individual intelligence.

Lecture slides from the "theory of everything" talk.

A comment on the "Theory of Everything" talk referenced by last Friday's post inquired if the whole lecture content was available.  Jim Pawley has been kind enough to forward two PDF files that contain the slides shown at the talk so that those interested could download them.  The first PDF is 10.2 MB in zie,  the second PDF is 2.8 MB in size.

Followup on MindBlog's Istanbul lecture on our subjective "I"

A previous post has pointed to a web text version of the piano recital and lecture I gave at "Cognitive VII", an international cognitive neuroscience meeting held in Istanbul May 18-20 of this year. The organizers indicated they would send a video of the piano performance and lecture, and after a number of tries, I have finally received, and now posted,  a video. It is missing a short bit of audio just after the beginning, and unfortunately deletes the last part of the talk on emotions and the evolution of music.  Still, it gives you a taste of the setting.

Serotonin regulates our moral judgements

Crockett et al. have done some fascinating experiments demonstrating that increased serotonin makes individuals less likely to endorse moral scenarios that result in the infliction of personal harm to others. They examine the effects of a single high dose of the selective serotonin reuptake inhibitor (SSRI) citalopram on moral judgment in healthy volunteers using a set of hypothetical scenarios portraying highly emotionally salient personal and less emotionally salient impersonal moral dilemmas with similar utilitarian outcomes (e.g., pushing a person in front of a train to prevent it from hitting five people and flipping a switch to divert a train to hit one person instead of five people, respectively). Here is their abstract:

Aversive emotional reactions to real or imagined social harms infuse moral judgment and motivate prosocial behavior. Here, we show that the neurotransmitter serotonin directly alters both moral judgment and behavior through increasing subjects’ aversion to personally harming others. We enhanced serotonin in healthy volunteers with citalopram (a selective serotonin reuptake inhibitor) and contrasted its effects with both a pharmacological control treatment and a placebo on tests of moral judgment and behavior. We measured the drugs' effects on moral judgment in a set of moral 'dilemmas' pitting utilitarian outcomes (e.g., saving five lives) against highly aversive harmful actions (e.g., killing an innocent person). Enhancing serotonin made subjects more likely to judge harmful actions as forbidden, but only in cases where harms were emotionally salient. This harm-avoidant bias after citalopram was also evident in behavior during the ultimatum game, in which subjects decide to accept or reject fair or unfair monetary offers from another player. Rejecting unfair offers enforces a fairness norm but also harms the other player financially. Enhancing serotonin made subjects less likely to reject unfair offers. Furthermore, the prosocial effects of citalopram varied as a function of trait empathy. Individuals high in trait empathy showed stronger effects of citalopram on moral judgment and behavior than individuals low in trait empathy. Together, these findings provide unique evidence that serotonin could promote prosocial behavior by enhancing harm aversion, a prosocial sentiment that directly affects both moral judgment and moral behavior.

A commentary by Tost and Meyer-Lindgerg notes:

In a broader context, the work by Crockett et al. supports a number of interesting conclusions. It extends prior evidence suggesting that there are at least two major pharmacological routes that modulate human social behavior: a direct route (“bottom-up”) involving prosocial neuropeptides such as oxytocin and vasopressin, which promote prosocial behaviors such as attachment, empathy, and generosity, and an indirect route (“top-down”) involving serotonin, which delimits antisocial behaviors by reducing negative affect and enhancing the aversiveness of harming others (see figure below). If this is true, functional interactions between these transmitter systems are likely. Consistent with this, Crockett et al. report a pronounced impact of serotonin augmentation on social decision making in subjects with high trait empathy, a finding suggestive of additive prosocial effects of both routes. The study also demonstrates that the effects of serotonin on prosocial behavior are relatively specific and are absent under norepinephrine augmentation with atomoxetine.

Figure - Regulatory circuits of social-emotional information processing in humans. “Top-down” control of the amygdala (AMY) arises from the anterior cingulate cortex (ACG) and ventral medial prefrontal cortex (vmPFC), with the latter being particularly important for the regulation of moral behaviors. “Bottom-up” modulation arises from neurons in the hypothalamus (HYP) expressing the neuropeptides oxytocin and vasopressin, which target distinct neuronal populations in the central amygdala. Projections from the amygdala to the brainstem, via the hypothalamus, regulate the expression of autonomic reactions to social signals. PFC, prefrontal cortex.