The representation of mood in primate anterior insular cortex

Understanding how the brain reflects and shapes mood requires resolving the disconnect between behavioral measures of mood that can only be made in humans (typically based on subjective reports of happiness) and detailed measures of brain activity only available in animals. To achieve this, we developed a mood model to predict behavioral fluctuations in human subjective happiness as individuals experienced wins and losses during a gambling task. Next, we investigated how this operationalization of mood was reflected behaviorally and in the brains of two monkeys engaged in the same gambling task. We found a remarkable alignment between human mood model signatures, the impact of estimated mood on monkey choice, and the persistent responses of units in monkey anterior insular cortex -- including a matched timescale of integration across events. In comparison, the same signatures were only weakly reflected in lateral prefrontal cortex, suggesting that insular mood representations do not trivially follow from a signal broadcast to all higher brain areas. These results are consistent with a model in which the brain transforms experiences into mood by integrating events through a recurrently connected network of excitatory and inhibitory pools of neurons. These are among the first detailed insights into the nature of putative mood representations in the primate brain.