C-tactile afferents C-tactile fibers Humanities Social interaction affect-regulating massage therapy affective touch anhedonia athlete's sex body psychotherapy chronic back pain current emotional state depression fMRI fibromyalgia integrative psychotherapy interoception massage therapy mood motivational system orienting reflex oxytocin pain posterior insula psychoactive massage somatic psychology somatic symptom disorder (DSM-5) somatoform pain (ICD 10) sports massage therapist's sex touch