Socially relative reward valuation in the primate brain

Evaluating the Influence of Musical and Monetary Rewards on Decision Making through Computational Modelling

A central question in behavioural neuroscience is how different rewards modulate learning. While the role of monetary rewards is well-studied in decision-making research, the influence of abstract rewards like music remains poorly understood. This study investigated the dissociable effects of these two reward types on decision making. Forty participants completed two decision-making tasks, each characterised by probabilistic associations between stimuli and rewards, with probabilities changing over time to reflect environmental volatility. In each task, choices were reinforced either by monetary outcomes (win/lose) or by the endings of musical melodies (consonant/dissonant). We applied the Hierarchical Gaussian Filter, a validated hierarchical Bayesian framework, to model learning under these two conditions. Bayesian statistics provided evidence for similar learning patterns across both reward types, suggesting individuals' similar adaptability. However, within the musical task, individual preferences for consonance over dissonance explained some aspects of learning. Specifically, correlation analyses indicated that participants more tolerant of dissonance behaved more stochastically in their belief-to-response mappings and were less likely to choose the response associated with the current prediction for a consonant ending, driven by higher volatility estimates. By contrast, participants averse to dissonance showed increased tonic volatility, leading to larger updates in reward tendency beliefs.

Chemogenetic dissection of a prefrontal-hypothalamic circuit for socially subjective reward valuation in macaques

The value of one's own reward is affected by the reward of others, serving as a source for envy. However, it is not known which neural circuits mediate such socially subjective value modulation. Here, we chemogenetically dissected the circuit from the medial prefrontal cortex (MPFC) to the lateral hypothalamus (LH) while male macaques were presented with visual stimuli that concurrently signaled the prospects of one's own and others' rewards. We found that functional disconnection between the MPFC and LH rendered animals significantly less susceptible to others' but not one's own reward prospects. In parallel with this behavioral change, inter-areal coordination, as indexed by coherence and Granger causality, decreased primarily in the delta and theta bands. These findings demonstrate that the MPFC-to-LH circuit plays a crucial role in carrying information about upcoming other-rewards for subjective reward valuation in social contexts.

Social comparisons differentially affect fair and unfair processing in ultimatum bargaining

Several theoretical frameworks have attempted to illustrate the influence of social contexts on decision-making and well-being. Traditional economic models assume that absolute income is the crucial determinant of one's well-being, while the comparative models state that social comparisons influence well-being and decisions. Here we investigated the impact of social comparisons on decision-making using a modified three-player Ultimatum Game and ERP technique. We found two independent effects: First, social comparisons did not affect decision-making when a fair norm was enforced. Second, social comparisons affected fairness consideration for unfair offers only-responders were less likely to accept unfair offers in upward comparisons but more likely to accept unfair offers in downward comparisons. These results revealed that people were envy-free of fair offers while affected mainly by social comparisons when the equality norm was broken. Event-related brain potentials showed that in the early time window (260-320 ms), compared to fair offers, unfair offers elicited a larger negative-going medial frontal negativity (MFN) in upward than parallel and downward comparisons, and in the late stage (320-650 ms), compared to fair offers, unfair offers led to equally less positive-going P300 in upward and downward comparisons relative to parallel comparison. Although partly consistent with the relative standing assumption, both traditional economic models and comparative models require revision to account for the results.

Reduced childhood social attention in autism model marmosets predicts impaired social skills and inflexible behavior in adulthood

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social and communication impairments and restricted and repetitive behavior. Although there is currently no established cure for ASD, early interventions for deficits of attention to other individuals are expected to reduce the progression of ASD symptoms in later life. To confirm this hypothesis and improve early therapeutic interventions, it is desirable to develop an animal model of ASD in which social attention is impaired in childhood and ASD-like social behavior is observed in adulthood. However, rodent models of ASD have difficulty in recapitulating the deficit of gaze-based social attention. In this study, we examined the direction of gaze toward other conspecifics during childhood and puberty in a three-chamber test setting using an ASD marmoset model produced by maternal exposure to valproic acid (VPA). We also conducted a reversal learning test in adult VPA-exposed marmosets as an indicator of perseveration, a core symptom of ASD that has not previously been investigated in this model. The results showed that time spent gazing at other conspecifics was reduced in VPA-exposed marmosets in childhood, and that mature animals persisted with previous strategies that required long days for acquisition to pass the test. In a longitudinal study using the same animals, deficits in social attention in childhood correlated well with ASD-like social disturbance (inequity aversion and third-party reciprocity) and inflexible behavior in adulthood. Since VPA-exposed marmosets exhibit these diverse ASD-like behaviors that are consistent from childhood to adulthood, VPA-exposed marmosets will provide a valuable means of elucidating mechanisms for early intervention and contribute to the development of early therapies.