Sociobiology: Changing the Dominance Hierarchy

One fundamental question is to understand what neural circuits are involved when social hierarchies are established, maintained and modified. Now, a new study shows that a previously subordinate animal can become dominant after optogenetic stimulation of the dorsomedial prefrontal cortex, demonstrating that this brain region is necessary and sufficient to quickly induce winning during social competitions.

Effect of the catechol-O-methyltransferase Val 158 Met polymorphism on theory of mind in obesity

Obesity is often accompanied with psychosocial adjustment problems, such as difficulties in social interactions and social withdrawal. A key aspect of social cognition is theory of mind, which allows inferring mental states, feelings, motivations, and beliefs of others and to use this information to predict their future behaviour. Theory of mind is highly dependent on prefrontal dopaminergic neurotransmission, which is regulated by catechol-O-methyltransferase (COMT) activity. We aimed at determining whether theory of mind is altered in obesity and if this ability is modulated by COMT. Fifty patients with obesity and 47 normal-weight individuals underwent the Reading the Mind in the Eyes Test, the Wisconsin Card Sorting Test, and the Vocabulary subscale of the Wechsler Adult Intelligence Scale. The genotype for the COMT Val ¹⁵⁸ Met functional polymorphism was determined for all subjects. Patients with obesity obtained significantly lower scores in the negative items of the Reading the Mind in the Eyes Test than normal-weight subjects. Further, an interaction effect was observed between group and COMT genotype. Specifically, the presence of the Met allele was associated to a better identification of negative mental states only in patients with obesity. Our results indicate that obesity is accompanied with difficulties in theory of mind and that this ability is influenced by the COMT genotype.

Spreading inequality: neural computations underlying paying-it-forward reciprocity

People tend to pay the generosity they receive from a person forward to someone else even if they have no chance to reciprocate directly. This phenomenon, known as paying-it-forward (PIF) reciprocity, crucially contributes to the maintenance of a cooperative human society by passing kindness among strangers and has been widely studied in evolutionary biology. To further examine its neural implementation and underlying computations, we used functional magnetic resonance imaging together with computational modeling. In a modified PIF paradigm, participants first received a monetary split (i.e. greedy, equal or generous) from either a human partner or a computer. They then chose between two options involving additional amounts of money to be allocated between themselves and an uninvolved person. Behaviorally, people forward the previously received greed/generosity towards a third person. The social impact of previous treatments is integrated into computational signals in the ventromedial prefrontal cortex and the right temporoparietal junction during subsequent decision making. Our findings provide insights to understand the proximal origin of PIF reciprocity.

A causal role for right temporo-parietal junction in signaling moral conflict

The right temporo-parietal junction (rTPJ) has been proposed to play a key role in guiding human altruistic behavior, but its precise functional contribution to altruism remains unclear. We aimed to disentangle three possible functions of the rTPJ for human altruism, namely: implementing the motivation to help, signaling conflicts between moral and material values, or representing social reputation concerns. Our novel donation-decision task consisted of decisions requiring trade-offs of either positive moral values and monetary cost when donating to a good cause, or negative moral values and monetary benefits when sending money to a bad cause. Disrupting the rTPJ using transcranial magnetic stimulation did not change the general motivation to give or to react to social reputation cues, but specifically reduced the behavioral impact of moral-material conflicts. These findings reveal that signaling moral-material conflict is a core rTPJ mechanism that may contribute to a variety of human moral behaviors.

Differences in Cortical Structure and Functional MRI Connectivity in High Functioning Autism

Autism spectrum disorders (ASD) represent a complex group of neurodevelopmental conditions characterized by deficits in communication and social behaviors. We examined the functional connectivity (FC) of the default mode network (DMN) and its relation to multimodal morphometry to investigate superregional, system-level alterations in a group of 22 adolescents and young adults with high-functioning autism compared to age-, and intelligence quotient-matched 29 healthy controls. The main findings were that ASD patients had gray matter (GM) reduction, decreased cortical thickness and larger cortical surface areas in several brain regions, including the cingulate, temporal lobes, and amygdala, as well as increased gyrification in regions associated with encoding visual memories and areas of the sensorimotor component of the DMN, more pronounced in the left hemisphere. Moreover, patients with ASD had decreased connectivity between the posterior cingulate cortex, and areas of the executive control component of the DMN and increased FC between the anteromedial prefrontal cortex and areas of the sensorimotor component of the DMN. Reduced cortical thickness in the right inferior frontal lobe correlated with higher social impairment according to the scores of the Autism Diagnostic Interview-Revised (ADI-R). Reduced cortical thickness in left frontal regions, as well as an increased cortical thickness in the right temporal pole and posterior cingulate, were associated with worse scores on the communication domain of the ADI-R. We found no association between scores on the restrictive and repetitive behaviors domain of ADI-R with structural measures or FC. The combination of these structural and connectivity abnormalities may help to explain some of the core behaviors in high-functioning ASD and need to be investigated further.

Integration of individual and social information for decision-making in groups of different sizes

When making judgments in a group, individuals often revise their initial beliefs about the best judgment to make given what others believe. Despite the ubiquity of this phenomenon, we know little about how the brain updates beliefs when integrating personal judgments (individual information) with those of others (social information). Here, we investigated the neurocomputational mechanisms of how we adapt our judgments to those made by groups of different sizes, in the context of jury decisions for a criminal. By testing different theoretical models, we showed that a social Bayesian inference model captured changes in judgments better than 2 other models. Our results showed that participants updated their beliefs by appropriately weighting individual and social sources of information according to their respective credibility. When investigating 2 fundamental computations of Bayesian inference, belief updates and credibility estimates of social information, we found that the dorsal anterior cingulate cortex (dACC) computed the level of belief updates, while the bilateral frontopolar cortex (FPC) was more engaged in individuals who assigned a greater credibility to the judgments of a larger group. Moreover, increased functional connectivity between these 2 brain regions reflected a greater influence of group size on the relative credibility of social information. These results provide a mechanistic understanding of the computational roles of the FPC-dACC network in steering judgment adaptation to a group’s opinion. Taken together, these findings provide a computational account of how the human brain integrates individual and social information for decision-making in groups.

In collective decisions, both the size of groups and the confidence that each member has in their own judgment determine how much a given individual will adapt to the judgment of the group. Here, we show that judgment adaptation during collective decisions—a fundamental brain mechanism needed for fluid functioning of social organizations—can be accounted for by Bayesian inference computations. At the time of judgment adaptation, individuals trade off the credibility inferred from their own confidence levels against the credibility of social information. The dorsal anterior cingulate cortex (dACC) represented belief updates, while the lateral frontopolar cortex (FPC) monitored the changes in credibility assigned to social information. These results provide a neurocomputational understanding of how individuals benefit both from the wisdom of larger groups and from their own confidence.

Social brains and divides: the interplay between social dominance orientation and the neural sensitivity to hierarchical ranks

Ubiquitous in the animal kingdom, dominance hierarchies emerge through social competition and underlie the control of resources. Confronting the disruptive influence of socioeconomic inequalities, human populations tend to split into groups who legitimize existing dominance hierarchies and groups who condemn them. Here, we hypothesized that variations in the neural sensitivity to dominance ranks partly underpins this ideological split, as measured by the social dominance orientation scale (SDO). Following a competitive task used to induce dominance representations about three opponents (superior, equal and inferior), subjects were passively presented the faces of these opponents while undergoing fMRI. Analyses demonstrated that two key brain regions, the superior temporal sulcus (STS) and anterior dorsolateral prefrontal cortex (aDLPFC) were sensitive to social ranks. Confirming our hypothesis, the sensitivity of the right aDLPFC to social ranks correlated positively with the SDO scale, which is known to predict behaviors and political attitudes associated with the legitimization of dominance hierarchies. This study opens new perspectives for the neurosciences of political orientation and social dominance.

The neural dynamics of reward value and risk coding in the human orbitofrontal cortex

The orbitofrontal cortex is known to carry information regarding expected reward, risk and experienced outcome. Yet, due to inherent limitations in lesion and neuroimaging methods, the neural dynamics of these computations has remained elusive in humans. Here, taking advantage of the high temporal definition of intracranial recordings, we characterize the neurophysiological signatures of the intact orbitofrontal cortex in processing information relevant for risky decisions. Local field potentials were recorded from the intact orbitofrontal cortex of patients suffering from drug-refractory partial epilepsy with implanted depth electrodes as they performed a probabilistic reward learning task that required them to associate visual cues with distinct reward probabilities. We observed three successive signals: (i) around 400 ms after cue presentation, the amplitudes of the local field potentials increased with reward probability; (ii) a risk signal emerged during the late phase of reward anticipation and during the outcome phase; and (iii) an experienced value signal appeared at the time of reward delivery. Both the medial and lateral orbitofrontal cortex encoded risk and reward probability while the lateral orbitofrontal cortex played a dominant role in coding experienced value. The present study provides the first evidence from intracranial recordings that the human orbitofrontal cortex codes reward risk both during late reward anticipation and during the outcome phase at a time scale of milliseconds. Our findings offer insights into the rapid mechanisms underlying the ability to learn structural relationships from the environment.

Hormonal treatment increases the response of the reward system at the menopause transition: a counterbalanced randomized placebo-controlled fMRI study

Preclinical research using rodent models demonstrated that estrogens play neuroprotective effects if they are administered during a critical period near the time of cessation of ovarian function. In women, a number of controversial epidemiological studies reported that a neuroprotective effect of estradiol may be obtained on cognition and mood-related disorders if hormone therapy (HT) begins early at the beginning of menopause. Yet, little is known about the modulatory effects of early HT administration on brain activation near menopause. Here, we investigated whether HT, initiated early during the menopause transition, increases the response of the reward system, a key brain circuit involved in motivation and hedonic behavior. We used fMRI and a counterbalanced, double-blind, randomized and crossover placebo-controlled design to investigate whether sequential 17β-estradiol plus oral progesterone modulate reward-related brain activity. Each woman was scanned twice while presented with images of slot machines, once after receiving HT and once under placebo. The fMRI results demonstrate that HT, relative to placebo, increased the response of the striatum and ventromedial prefrontal cortex, two areas that have been shown to be respectively involved during reward anticipation and at the time of reward delivery. Our neuroimaging results bridge the gap between animal studies and human epidemiological studies of HT on cognition. These findings establish a neurobiological foundation for understanding the neurofunctional impact of early HT initiation on reward processing at the menopause transition.

A common currency for the computation of motivational values in the human striatum

Reward comparison in the brain is thought to be achieved through the use of a 'common currency', implying that reward value representations are computed on a unique scale in the same brain regions regardless of the reward type. Although such a mechanism has been identified in the ventro-medial prefrontal cortex and ventral striatum in the context of decision-making, it is less clear whether it similarly applies to non-choice situations. To answer this question, we scanned 38 participants with fMRI while they were presented with single cues predicting either monetary or erotic rewards, without the need to make a decision. The ventral striatum was the main brain structure to respond to both cues while showing increasing activity with increasing expected reward intensity. Most importantly, the relative response of the striatum to monetary vs erotic cues was correlated with the relative motivational value of these rewards as inferred from reaction times. Similar correlations were observed in a fronto-parietal network known to be involved in attentional focus and motor readiness. Together, our results suggest that striatal reward value signals not only obey to a common currency mechanism in the absence of choice but may also serve as an input to adjust motivated behaviour accordingly.

Endogenous cortisol levels are associated with an imbalanced striatal sensitivity to monetary versus non-monetary cues in pathological gamblers

Pathological gambling is a behavioral addiction characterized by a chronic failure to resist the urge to gamble. It shares many similarities with drug addiction. Glucocorticoid hormones including cortisol are thought to play a key role in the vulnerability to addictive behaviors, by acting on the mesolimbic reward pathway. Based on our previous report of an imbalanced sensitivity to monetary versus non-monetary incentives in the ventral striatum of pathological gamblers (PGs), we investigated whether this imbalance was mediated by individual differences in endogenous cortisol levels. We used functional magnetic resonance imaging (fMRI) and examined the relationship between cortisol levels and the neural responses to monetary versus non-monetary cues, while PGs and healthy controls were engaged in an incentive delay task manipulating both monetary and erotic rewards. We found a positive correlation between cortisol levels and ventral striatal responses to monetary versus erotic cues in PGs, but not in healthy controls. This indicates that the ventral striatum is a key region where cortisol modulates incentive motivation for gambling versus non-gambling related stimuli in PGs. Our results extend the proposed role of glucocorticoid hormones in drug addiction to behavioral addiction, and help understand the impact of cortisol on reward incentive processing in PGs.

Neural dynamics of reward probability coding: a Magnetoencephalographic study in humans

Prediction of future rewards and discrepancy between actual and expected outcomes (prediction error) are crucial signals for adaptive behavior. In humans, a number of fMRI studies demonstrated that reward probability modulates these two signals in a large brain network. Yet, the spatio-temporal dynamics underlying the neural coding of reward probability remains unknown. Here, using magnetoencephalography, we investigated the neural dynamics of prediction and reward prediction error computations while subjects learned to associate cues of slot machines with monetary rewards with different probabilities. We showed that event-related magnetic fields (ERFs) arising from the visual cortex coded the expected reward value 155 ms after the cue, demonstrating that reward value signals emerge early in the visual stream. Moreover, a prediction error was reflected in ERF peaking 300 ms after the rewarded outcome and showing decreasing amplitude with higher reward probability. This prediction error signal was generated in a network including the anterior and posterior cingulate cortex. These findings pinpoint the spatio-temporal characteristics underlying reward probability coding. Together, our results provide insights into the neural dynamics underlying the ability to learn probabilistic stimuli-reward contingencies.

Imbalance in the sensitivity to different types of rewards in pathological gambling

Pathological gambling is an addictive disorder characterized by a persistent and compulsive desire to engage in gambling activities. This maladaptive behaviour has been suggested to result from a decreased sensitivity to experienced rewards, regardless of reward type. Alternatively, pathological gambling might reflect an imbalance in the sensitivity to monetary versus non-monetary incentives. To directly test these two hypotheses, we examined how the brain reward circuit of pathological gamblers responds to different types of rewards. Using functional magnetic resonance imaging, we compared the brain responses of 18 pathological gamblers and 20 healthy control subjects while they engaged in a simple incentive task manipulating both monetary and visual erotic rewards. During reward anticipation, the ventral striatum of pathological gamblers showed a differential response to monetary versus erotic cues, essentially driven by a blunted reactivity to cues predicting erotic stimuli. This differential response correlated with the severity of gambling symptoms and was paralleled by a reduced behavioural motivation for erotic rewards. During reward outcome, a posterior orbitofrontal cortex region, responding to erotic rewards in both groups, was further recruited by monetary gains in pathological gamblers but not in control subjects. Moreover, while ventral striatal activity correlated with subjective ratings assigned to monetary and erotic rewards in control subjects, it only correlated with erotic ratings in gamblers. Our results point to a differential sensitivity to monetary versus non-monetary rewards in pathological gambling, both at the motivational and hedonic levels. Such an imbalance might create a bias towards monetary rewards, potentially promoting addictive gambling behaviour.

Neural coding of computational factors affecting decision making

We constantly need to make decisions that can result in rewards of different amounts with different probabilities and at different timing. To characterize the neural coding of such computational factors affecting value-based decision making, we have investigated how reward information processing is influenced by parameters such as reward magnitude, probability, delay, effort, and uncertainty using either fMRI in healthy humans or intracranial recordings in patients with epilepsy. We decomposed brain signals modulated by these computational factors, showing that prediction error (PE), salient PE, and uncertainty signals are computed in partially overlapping brain circuits and that both transient and sustained uncertainty signals coexist in the brain. When investigating the neural representation of primary and secondary rewards, we found both a common brain network, including the ventromedial prefrontal cortex and ventral striatum, and a functional organization of the orbitofrontal cortex according to reward type. Moreover, separate valuation systems were engaged for delay and effort costs when deciding between options. Finally, genetic variations in dopamine-related genes influenced the response of the reward system and may contribute to individual differences in reward-seeking behavior and in predisposition to neuropsychiatric disorders.

The architecture of reward value coding in the human orbitofrontal cortex

To ensure their survival, animals exhibit a number of reward-directed behaviors, such as foraging for food or searching for mates. This suggests that a core set of brain regions may be shared by many species to process different types of rewards. Conversely, many new brain areas have emerged over the course of evolution, suggesting potential specialization of specific brain regions in the processing of more recent rewards such as money. Here, using functional magnetic resonance imaging in humans, we identified the common and distinct brain systems processing the value of erotic stimuli and monetary gains. First, we provide evidence that a set of neural structures, including the ventral striatum, anterior insula, anterior cingulate cortex, and midbrain, encodes the subjective value of rewards regardless of their type, consistent with a general hedonic representation. More importantly, our results reveal reward-specific representations in the orbitofrontal cortex (OFC): whereas the anterior lateral OFC, a phylogenetically recent structure, processes monetary gains, the posterior lateral OFC, phylogenetically and ontogenetically older, processes more basic erotic stimuli. This dissociation between OFC representations of primary and secondary rewards parallels current views on lateral prefrontal cortex organization in cognitive control, suggesting an increasing trend in complexity along a postero-anterior axis according to more abstract representations. Together, our results support a modular view of reward value coding in the brain and propose that a unifying principle of postero-anterior organization can be applied to the OFC.

Damage to the fronto-polar cortex is associated with impaired multitasking

Background

A major question in understanding the functional organization of the brain is to delineate the functional divisions of the prefrontal cortex. Of particular importance to the cognitive capacities that are uniquely human is the fronto-polar cortex (Brodmann's area 10), which is disproportionally larger in humans relative to the rest of the brain than it is in the ape's brain. The specific function of this brain region remains poorly understood, but recent neuroimaging studies have proposed that it may hold goals in mind while exploring and processing secondary goals.

Principal Findings

Here we show that the extent of damage to the fronto-polar cortex predicts impairment in the management of multiple goals. This result reveals that the integrity of the fronto-polar cortex is necessary to perform tasks that require subjects to maintain a primary goal in mind while processing secondary goals, an ability which is crucial for complex human cognitive abilities.

Conclusion/Significance

These results provide important new insights concerning the cerebral basis of complex human cognition such as planning and multitasking.

Hormonal and Genetic Influences on Processing Reward and Social Information

Social neuroscience is an emerging interdisciplinary field that combines tools from cognitive, cellular, and molecular neuroscience to understand the neural mechanisms underlying human interactions, emphasizing the complementary nature of different organization levels in the social and biological domains. Previous studies focused on the molecular/neuronal substrates of a variety of complex behaviors, such as parental behavior and pair bonding. Less is known about the various factors influencing interindividual differences in reward processing and decision making in social contexts, both relying upon the dopaminergic system. This review concerns (1) basic electrophysiological findings and recent neuroimaging findings showing that reward processing and social interaction processes share common neural substrates and (2) genetic and hormonal influences on these processes. Recent research combining molecular genetics, endocrinology, and neuroimaging demonstrated that variations in dopamine-related genes and in hormone levels affect the physiological properties of the dopaminergic system in nonhuman primates and modulate the processing of reward and social information in humans. These findings are important because they indicate the neural influence of genes conferring vulnerability to develop neuropathologies such as drug addiction and pathological gambling. Taken together, the reviewed data start to unveil the relationships between genes, hormones, and the functioning of the reward system, as well as decision making in social contexts, and provide a link between molecular, cellular, and social cognitive levels in humans.

Silence is golden: transient neural deactivation in the prefrontal cortex during attentive reading

It is becoming increasingly clear that attention-demanding tasks engage not only activation of specific cortical regions but also deactivation of other regions that could interfere with the task at hand. At the same time, electrophysiological studies in animals and humans have found that the participation of cortical regions to cognitive processes translates into local synchronization of rhythmic neural activity at frequencies above 40 Hz (so-called gamma-band synchronization). Such synchronization is seen as a potential facilitator of neural communication and synaptic plasticity. We found evidence that cognitive processes can also involve the disruption of gamma-band activity in high-order brain regions. Intracerebral electroencephalograms were recorded in 3 epileptic patients during 2 reading tasks. Visual presentation of words induced a strong deactivation in a broad (20-150 Hz) frequency range in the left ventral lateral prefrontal cortex, in parallel with gamma-band activations within the reading network, including Broca's area. The observed energy decrease in neural signals was reproducible across patients. It peaked around 500 ms after stimulus onset and appeared subject to attention-modulated amplification. Our results suggest that cognition might be mediated by a coordinated interaction between regional gamma-band synchronizations and desynchronizations, possibly reflecting enhanced versus reduced local neural communication.

Sensitivity of the brain to loss aversion during risky gambles

Little is known about the neural systems that subserve human loss aversion. A recent neuroimaging study by Tom, Poldrack and colleagues reports that this pattern of behaviour is directly tied to the greater sensitivity of the brain to potential losses compared with potential gains and uncovers a brain network whose activity increases with potential gains and decreases with potential losses. These results challenge the common view that loss aversion engages a distinct emotion-related brain network (e.g. amygdala and insula).