Body mapping of cutaneous wetness perception across the human torso during thermo-neutral and warm environmental exposures

Abstract

Sensing skin wetness is linked to inputs arising from cutaneous cold-sensitive afferents. As thermosensitivity to cold varies significantly across the torso, we investigated whether similar regional differences in wetness perception exist. We also investigated the regional differences in thermal pleasantness and whether these sensory patterns are influenced by ambient temperature. Sixteen males (20 ± 2 yr) underwent a quantitative sensory test under thermo-neutral [air temperature (Tair) = 22°C; relative humidity (RH) = 50%] and warm conditions (Tair = 33°C; RH = 50%). Twelve regions of the torso were stimulated with a dry thermal probe (25 cm(2)) with a temperature of 15°C below local skin temperature (Tsk). Variations in Tsk, thermal, wetness, and pleasantness sensations were recorded. As a result of the same cold-dry stimulus, the skin-cooling response varied significantly by location (P = 0.003). The lateral chest showed the greatest cooling (-5 ± 0.4°C), whereas the lower back showed the smallest (-1.9 ± 0.4°C). Thermal sensations varied significantly by location and independently from regional variations in skin cooling with colder sensations reported on the lateral abdomen and lower back. Similarly, the frequency of perceived skin wetness was significantly greater on the lateral and lower back as opposed to the medial chest. Overall wetness perception was slightly higher under warm conditions. Significantly more unpleasant sensations were recorded when the lateral abdomen and lateral and lower back were stimulated. We conclude that humans present regional differences in skin wetness perception across the torso, with a pattern similar to the regional differences in thermosensitivity to cold. These findings indicate the presence of a heterogeneous distribution of cold-sensitive thermo-afferent information.

Neurophysiology of Skin Thermal Sensations

“…For example, cold sensitivity across the torso seems to vary significantly, with regions such as the lateral abdomen and lower back presenting higher sensitivity than upper torso regions ( Fig. 3) (99). The body maps pictured in figure 3 present data from one of this author's recent studies (99).…”

“…3) (99). The body maps pictured in figure 3 present data from one of this author's recent studies (99). In the mentioned study, thermal sensations resulting from the application of a standardized cold stimulus (i.e.…”

“…Furthermore, the regional distribution of cold sensitivity has been shown not only to be higher on the torso than e.g. on the limbs (238), but to also vary largely within this region (99,238). For example, cold sensitivity across the torso seems to vary significantly, with regions such as the lateral abdomen and lower back presenting higher sensitivity than upper torso regions ( Fig.…”

“…thermal and tactile) underlie the ability to perceive skin wetness, has also to led to the investigation of the potential regional variability in skin wetness sensitivity across the body, and of its relationship with what known with regards to the regional differences in sensitivity observed in other somatosensory modalities (e.g. thermal sensitivity) (1,99,100,109,120,191). As a result, we now know that, during the contact with external stimuli, as well as a result of sweating, skin wetness can be perceived to a larger extent on certain regions of hairy skin (e.g.…”

Tactile cues significantly modulate the perception of sweat-induced skin wetness independently of the level of physical skin wetness

“…This hypothesis has been supported by our previous findings. We have repeatedly shown that the central integration of cold sensations (primarily resulting from the afferent activity of cutaneous cold-sensitive, thinly-myelinated A␦-nerve fibers) (DarianSmith 1984) and of tactile inputs (encoded by cutaneous mechano-sensitive A␤-nerve fibers) (Tsunozaki and Bautista 2009) plays a critical role in the ability to perceive skin wetness (Filingeri et al 2013(Filingeri et al , 2014a(Filingeri et al , 2014b(Filingeri et al , 2014c. Indeed, we seem to interpret the coldness (i.e., thermal component) and stickiness (i.e., tactile component) experienced when the skin is wet as a signal of the presence of moisture (and thus wetness) on the skin's surface.…”