Affective Touch: Psychophysics, Physiology and Vicarious Touch Perception

It is hypothesized that the affective quality of touch is conveyed through the stimulation of a group of unmyelinated low threshold mechanoreceptors (LTM) called C-Tactile afferents (CTs). Research has shown that CTs selectively respond to slow gentle stroking touch, delivered at skin temperature (~32 °C). Over the past three decades many studies have benefited from the development of bespoke psychophysical tools and methods to optimally stimulate these afferents, while controlling for activity in discriminative A-β afferents. More recently, the affective quality of CT-optimal touch has been measured using facial electromyography (EMG), allowing us to capture the more subtle affective responses to CT stimulation. One of the key arguments for this afferent being important for sociability is that the touch is vicariously experienced when we observe others receiving an optimal tactile stimulus. A series of studies have shown that cortical activity matches the activity elicited during first-hand touch, so we also discuss these video-based studies here.