The Role of the Primate Amygdala in Social and Affective Touch

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Touch is our first emotional language – the language that allows us to receive and understand affective signals and help lay the foundation for future social bonds. Despite the widely recognized importance of touch in brain development and in affective and social communication throughout life, remarkably little is known about its cellular neural substrate. Relatively recent discoveries showed that the skin contains specializations for detecting and evaluating the pleasantness of touch. It is unclear how these signals might be processed in the brain. It is clear, however, that the amygdala is required for processing the social and emotional significance of sensory stimuli, regardless of modality. Studies that showed this role of the primate amygdala focused almost exclusively on vision. Recently we have reported the presence of touch-responsive neurons in the primate amygdala. We will expand on this initial finding and determine how these touch-responsive cells respond to the basic sensory features of tactile stimuli: location and intensity (Aim 1). Next, we will determine whether tactile cells in the amygdala encode the subjective value of touch (Aim 2). Given the important role of the amygdala in processing social stimuli, we will then determine how the social dimension of touch factors into the activity of tactile cells (Aim 3). Specifically, we will simultaneously monitor neural responses to touch in the amygdala and somatosensory cortex and compare neural responses to the same type of social touch, delivered to the same skin area, by two individuals with whom the recipient has a different social experience. We expect tactile cells in the amygdala, but not in the somatosensory cortex, to discriminate between social partners, supporting the idea that the amygdala extracts the social-affective dimension (value) of stimuli. Collectively, these three aims provide a conceptually new and technically advanced physiological framework for understanding how the primate amygdala responds to and evaluates tactile stimuli that vary in subjective value and social significance. Understanding the cellular machinery of affective touch in the primate brain is expected to provide important insights into why touch processing is so profoundly altered in functional pain syndromes, autism, and numerous other mental disorders.