The soft touches that arise from the gentler sweeping movements common during grooming may activate a class of unmyelinated afferent fibers (C-fibers) that project to both the limbic system and the orbito-frontal cortex. This route is quite distinct from the more conventional somatosensory routes (touch, pain, heat and itch) that underpin discriminative touch sensation and involve low threshold mechanoreceptors in the skin and large diameter A-beta fibers projecting to the sensory cortex. In contrast, the unmyelinated c-fibers appear to give rise to a pleasant sensation of light touch when skin is stroked lightly (Touch; 2007).
Pleasant touch gives rise to a different activation pattern in the human brain than neutral touch, notably activation of an area in the orbito-frontal cortex close to areas responding to pleasant taste and smell. In functional magnetic resonance imaging (fMRI) study, pleasant touch to the hand with velvet produced stronger activation of the orbito-frontal cortex than affectively neutral touch of the hand with wood. In contrast, the affectively neutral but more intense touch produced more activation of the primary somatosensory cortex than the pleasant stimulus. This indicates that part of the orbito-frontal cortex is concerned with representing the positively affective aspects of somatosensory stimuli (Pleasant touch; 1999).
A light touch stimulus, which was slowly moving over the hairy skin of the forearm, produced a strong activation of the insular cortex. Thus, the essential role of the sensory nerves system (C-afferents system) is to provide emotional and behavioral responses to affiliative or friendly skin-to-skin contact.
In humans, blood pressure is sensitive to supportive and non-supportive interactions between partners. Emotional support and affection in couples is expressed through physical touch, such as hand-holding, hugs, and sitting- or lying- cuddled up (Touch; 2010).
It has been shown that enhanced oxytocin (OXT) activity is one of the primary physiological mediators of the health benefits of emotional support, particularly those linked to warm touch. The frequent hugs between spouses/partners were associated with lower blood pressure and higher plasma OXT levels (Hug and OXT 2004).