Touch perceptions across skin sites: differences between sensitivity, direction discrimination and pleasantness

Abstract

Human skin is innervated with different tactile afferents, which are found at varying densities over the body. We investigate how the relationships between tactile pleasantness, sensitivity and discrimination differ across the skin. Tactile pleasantness was assessed by stroking a soft brush over the skin, using five velocities (0.3, 1, 3, 10, 30 cm s−1), known to differentiate hedonic touch, and pleasantness ratings were gained. The ratings velocity-profile is known to correlate with firing in unmyelinated C-tactile (CT) afferents. Tactile sensitivity thresholds were determined using monofilament force detection and the tactile discrimination level was obtained in the direction discrimination of a moving probe; both tasks readily activate myelinated touch receptors. Perceptions were measured over five skin sites: forehead, arm, palm, thigh and shin. The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1–10 cm s−1), where higher ratings were gained compared to the slowest and fastest velocities. This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen. We find that tactile sensitivity and discrimination vary across the skin, where the forehead and palm show increased acuity. Tactile sensitivity and discrimination levels also correlated significantly, although the tactile acuity did not relate to the perceived pleasantness of touch. Tactile pleasantness varied in a subtle way across skin sites, where the middle velocities were always rated as the most pleasant, but the ratings at hairy skin sites were more receptive to changes in stroking velocity. We postulate that although the mechanoreceptive afferent physiology may be different over the skin, the perception of pleasant touch can be interpreted using all of the available incoming somatosensory information in combination with central processing.

The manual orienting response habituation to repeated tactile stimuli in preterm neonates: Discrimination of stimulus locations and interstimulus intervals

“…Moreover, habituation was observed regardless of stimulus location (palm or forearm), confirmed by the absence of a group effect on the orienting response to the Familiarization period. Therefore, our results do not support a lower sensitivity or habituation ability of the forearm compared with the hand, as may be the case in adults (Ackerley, Carlsson, Wester, Olausson, & Backlund Wasling, ). This may be due to interindividual variability concealing smaller between groups differences.…”

“…Therefore, our results do not support a lower sensitivity or habituation ability of the forearm compared with the hand, as may be the case in adults (Ackerley, Carlsson, Wester, Olausson, & Backlund Wasling, 2014). This may be due to interindividual variability concealing smaller between groups differences.…”

C-tactile afferent stimulating touch carries a positive affective value

“…VAS scales ranging from unpleasant to pleasant have been shown in previous studies to provide a reliable and sensitive measure of differences in affective touch perception across stimuli and locations [15,33,34]. …”

Affective Touch Dimensions: From Sensitivity to Metacognition

“…Following the proposal of this hypothesis, a large body of research has focused on quantifying the sensory and emotional aspects of touch, including hairy and glabrous skin (Ackerley, Carlsson, Wester, Olausson, & Backlund Wasling, 2014;Ackerley, Saar, McGlone, & Backlund Wasling, 2014;Essick et al, 2010;Guest et al, 2011;Mcglone et al, 2012), and on conducting relevant neuroimaging studies to study the role of limbic and insular regions in the central processing of affective as opposed to neutral touch stimuli. For example, a growing body of research has characterised an affective touch network that appears to bypass the primary somatosensory area typically associated with the discriminatory aspects of touch S1 (c.f., Gazzola et al, 2012;Mccabe, Rolls, Bilderbeck, & McGlone, 2008) by activating brain regions implicated in the cognitive-affective aspects of the touch, such as the posterior superior temporal sulcus, medial prefrontal cortex orbitofrontal cortex (OFC) and anterior cingulate cortex (ACC) (Gordon et al, 2013).…”