Neurophysiology of pleasant touch: From peripheral mechanisms to clinical implications of caressing.

While tactile perception has long been studied through the lens of discriminative touch, recent research has highlighted the existence of a distinct affective touch system. Pleasant touch refers to specific forms of light tactile stimulation, such as gentle stroking or caressing applied to hairy skin. This type of sensation is primarily conveyed by unmyelinated C-tactile (CT) afferents expressing a subclass of mechanoreceptors with low-threshold activation and slow-to-intermediate adaptation. Importantly, CT firing correlates strongly with subjective pleasantness ratings but not with intensity or localization accuracy, indicating a preferential role in affective rather than perceptual encoding. After reaching the superficial layers of the dorsal horn of the spinal cord, the projections ascend via pathways associated with interoception. Following thalamic relay, pleasant tactile information induces strong activation of a vast network including the posterior and anterior insula, the orbitofrontal cortex, the medial prefrontal cortex, the anterior cingulate cortex, and the ventral striatum. The literature converges on the idea that pleasant touch relies on a specialized neurophysiological system integrating peripheral CT afferents, insular processing, and neurochemical modulation, mainly involving oxytocin, dopamine, and opioid transmission. It impacts on autonomic nervous system regulation and physiological homeostasis, as shown by anti-stress effects of skin-to-skin contact in infants. Affective touch conveyed by CT afferents supports emotional regulation, social bonding, and well-being. In addition, pleasant touch has a therapeutic potential, especially in the pain domain, but also in other conditions dominated by negative thoughts, such as depressive disorders. Thus, the clinical utility of "affective touch therapy", even by means of robotic haptic stimulation, offers promising prospects for the treatment of anxiety-depressive or pain disorders, based on the neurophysiological effects of CT afferent activation.