Differential and temporally dynamic involvement of primate amygdala nuclei in face animacy and reward information processing

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Decision-making is influenced by both expected reward and social factors, such as who offered the outcomes. Thus, although a reward might originally be independent from social factors, the two elements are closely related. However, whether and how they are processed separately or conjointly remains unclear. Here, we show that neurons in distinct sub-nuclei of the amygdala encode expected reward and face animacy, which is a vital aspect of face perception. Although these encoding processes are distinct, they rely on partially shared neuronal circuits with characteristic temporal dynamics.

Two male macaque monkeys made saccades under different social and reward contexts, created by presenting facial images with independent attributes: animacy (a monkey or cartoon face) and associated reward (large or small). The stimulus image was presented twice per trial: during the initial stimulus encoding (S1) and before saccades were made (S2). A longer gaze duration for eye region of the monkey versus cartoon images indicated more robust social engagement for realistic faces. During S1, a similar number of lateral nucleus neurons encoded either animacy only with a monkey-image preference, reward only with a large-reward preference, or both. Conversely, neurons in the basal and central nuclei primarily encoded reward, preferring large-versus small-reward associated face images. The reward-dependent modulation was continuous after S1, but was more conspicuous during S1 in the basal nucleus and during both S1 and S2 in the central nucleus. This anatomically- and temporally-specific encoding in the amygdala may underlie the computation and integration of face animacy and reward information.

Significance Statement

Reward and social information are closely related but originally independent, as both influence our decision-making. The amygdala has been associated with both reward and social information coding. However, whether and how they are processed separately or conjointly by individual neurons in the amygdala remains unclear.

We found that neurons in the lateral and basal nuclei encoded face animacy, which is an important aspect of social information, and reward, respectively, during sensory processing. Neurons in the central nucleus encoded reward information during the execution phase. This provides new clarity regarding the mechanisms of separate or integrated social and reward information processing within the amygdala.

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