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 universal 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 in the brains of two monkeys engaged in the same gambling task. We found a remarkable alignment between human mood model signatures 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 dorsolateral prefrontal cortex, suggesting that insular mood representations do not trivially follow from a signal (like arousal) 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.

Significance StatementHow does the brain shape mood? Answering this question is difficult because measures of mood require asking humans how they feel, but our best measures of brain activity are restricted to nonhuman animals. To overcome this challenge, we developed a model to link across these different types of data as human happiness fluctuated following wins and losses during a gambling game, and monkeys played the same game. We found a strong neural correlate of human happiness reflected in the persistent responses of neurons in monkey anterior insular cortex, a brain area implicated in the conscious experience of feelings. These results suggest that the brain may convert experiences into mood by integrating experiences through a network of recurrently connected neurons.