Summary Reinforcement learning (RL) theories posit that dopaminergic signals are integrated within the striatum to associate choices with outcomes. Often overlooked is that the amygdala also receives dopaminergic input and is involved in Pavlovian processes that influence choice behavior. To determine the relative contributions of the ventral striatum (VS) and amygdala to appetitive RL we tested rhesus macaques with VS or amygdala lesions on deterministic and stochastic versions of a two-arm bandit reversal learning task. When learning was characterized with a RL model relative to controls, amygdala lesions caused general decreases in learning from positive feedback and choice consistency. By comparison, VS lesions only affected learning in the stochastic task. Moreover, the VS lesions hastened the monkeys’ choice reaction times, which emphasized a speed-accuracy tradeoff that accounted for errors in deterministic learning. These results update standard accounts of RL by emphasizing distinct contributions of the amygdala and VS to RL.

The interaction between the behavioral and physiological immune systems provides fertile ground for research. Here, we examine the interactions between fear of disease, collectivism/individualism, disgust, visual perception and salivary IgA. First, we parsed collectivism/individualism into ancestry and psychological processes and examined their relationships to fear of disease. Both ancestral and psychological collectivists scored higher on a test of hypochondria than individualists. Additionally, in two studies we exposed participants to slides of diseased, injured or healthy individuals. Diseased and injured stimuli were rated as equally disgusting, while diseased stimuli were rated as more disgusting than healthy stimuli. We measured salivary IgA in participants before and after they viewed the stimuli. Participants provided information on their ancestral collectivism or individualism. Salivary IgA levels increased after participants viewed images of diseased or injured individuals. Participants with collectivist ancestry tended to react to the diseased and injured images with an increase in IgA, while levels of IgA remained the same or decreased in individualists in one study but we failed to replicate the effect in the second study. An increased salivary IgA response to potentially diseased individuals is adaptive, because salivary IgA plays an important role in protecting individuals from contracting an infection. The response may be related to increased preoccupation with disease states.

The evolutionary and neural underpinnings of human prosociality are still largely unknown. A growing body of evidence suggests that some species find the sight of another individual receiving a reward reinforcing, often called vicarious reinforcement. One hypothesis is that vicarious reward is reinforcing because it is arousing like a primary reward. We evaluated this hypothesis by measuring the autonomic pupil response of eight monkeys across two laboratories in two different versions of a vicarious reinforcement paradigm. Monkeys were cued as to whether an upcoming reward would be delivered to them, another monkey, or nobody and could accept or decline the offer. As expected, all monkeys in both laboratories showed a marked preference for juice to the self, together with a reliable prosocial preference for juice to a social partner compared to juice to nobody. However, contrary to the autonomic arousal hypothesis, we found that pupils were widest in anticipation of juice to the self, moderately-sized in anticipation of juice to nobody, and narrowest in anticipation of juice to a social partner. This effect was seen across both laboratories and regardless of specific task parameters. The seemingly paradoxical pupil effect can be explained by a model in which pupil size tracks outcome salience, prosocial tendencies track outcome valence, and the relation between salience and valence is U-shaped.

The evolutionary and neural underpinnings of human prosociality are still being identified. A growing body of evidence suggests that some species find the sight of another individual receiving a reward reinforcing, called vicarious reinforcement, and that this capacity is supported by a network of brain areas including the anterior cingulate cortex (ACC) and the amygdala. At the same time, analyses of autonomic arousal have been increasingly used to contextualize and guide neural research, especially for studies of reward processing. Here, we characterized the autonomic pupil response of eight monkeys across two laboratories in two different versions of a vicarious reinforcement paradigm. Monkeys were cued as to whether an upcoming reward would be delivered to them, another monkey, or nobody and could accept or decline the offer. As expected, all monkeys in both laboratories showed a marked preference for juice to the self, together with a reliable prosocial preference for juice to a social partner compared to juice to nobody. However, contrary to our expectations, we found that pupils were widest in anticipation of juice to the self, moderately sized in anticipation of juice to nobody, and narrowest in anticipation of juice to a social partner. This effect was seen across both laboratories and regardless of specific task parameters. The seemingly paradoxical pupil effect can be explained by a model in which pupil size tracks outcome salience, prosocial tendencies track outcome valence, and the relation between salience and valence is U-shaped.