C-tactile (CT) afferents: evidence of their function from microneurography studies in humans

Abstract

• Unmyelinated C-tactile afferents can be recorded in humans via microneurography. • They are highly sensitive mechanoreceptors, with low activation thresholds. • They respond vigorously to dynamic, moving touch. • They show characteristic responses to mechanical, thermal, and electrical stimuli. • C-tactile afferents are believed to convey positive affective aspects of touch. C-tactile (CT) afferents are low-threshold mechanoreceptors present in the skin of humans and are thought to convey positive and pleasant aspects of touch, due to their optimal firing during gentle, caress-like contact. This review explores their role and function through the evidence produced in microneurography studies, where it is possible to record from single CTs in awake, healthy humans. CTs send a relatively delayed signal to the brain, due to their unmyelinated, slowly conducting axon, and are highly sensitive to small displacements of the skin, especially from dynamic, moving touch. CTs are primarily mechanoreceptors, but show some thermal sensitivity, where neutral touch (at skin temperature ∼32°C) is optimal, warm touch (∼42°C) activates them less, and cool touch (∼18°C) produces complex responses.