Abstract: The amygdala plays a central role in emotion and social behavior, yet its role in processing social and affective touch has not been established. Tactile stimuli, processed initially by the somatosensory cortex, acquire affective salience downstream from early processing stages possibly in the amygdala. We monitored simultaneously neural activity in the somatosensory cortex and the amygdala of monkeys that received alternating blocks of either innocuous, gentle air puffs or grooming-like touch from a trusted trainer. We expected neurons in the somatosensory cortex to encode the physical features of puff and touch stimuli whereas neurons in the amygdala were expected to differentiate between the neutral, non-social puff and the pleasant, social touch. The pleasantness of touch was inferred from the autonomic state of the recipients. During grooming blocks, monkeys appeared less vigilant, closed their eyes, had lower heart rates, and increased vagal tone. In contrast, during periods of puff delivery, high levels of vigilance and sympathetic arousal were evident. Surprisingly, during grooming, neurons in the amygdala stopped responding to tactile stimuli, even if the stimuli were delivered to the same areas of the skin that showed reliable responses to puff. This suggests the presence of a gating mechanism in the amygdala. Instead of responding to each touch stimulus, a set of amygdala neurons signaled with sustained changes in baseline firing rate throughout the touch blocks. These finding suggest that while receiving affective touch, the amygdala may be decoupled from monitoring the external environment, while tonically signaling to the rest of the brain the social-behavioral context and affective state of the recipient.
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Dr. Gothard is a professor in the departments of Physiology and Neuroscience. The broad goal of our research is to understand the neural basis of emotion and social behavior. We work with rhesus monkeys because they share with humans social behaviors and the hierarchical organization of the societies. We place emphasis on exploring brain activity during natural or seminatural behaviors. For example, we monitor neural activity in the amygdala and in the somatosensory cortex while the monkeys receive social grooming and non-social tactile stimuli. Joint monitoring neural activity and autonomic reveal the real-time dynamic interactions between brain areas involved in social perception, decision-making and the control of overt social behaviors.