Human skin wetness perception: psychophysical and neurophysiological bases

Abstract

The ability to perceive thermal changes in the surrounding environment is critical for survival. However, sensing temperature is not the only factor among the cutaneous sensations to contribute to thermoregulatory responses in humans. Sensing skin wetness (i.e. hygrosensation) is also critical both for behavioral and autonomic adaptations. Although much has been done to define the biophysical role of skin wetness in contributing to thermal homeostasis, little is known on the neurophysiological mechanisms underpinning the ability to sense skin wetness. Humans are not provided with skin humidity receptors (i.e., hygroreceptors) and psychophysical studies have identified potential sensory cues (i.e. thermal and mechanosensory) which could contribute to sensing wetness. Recently, a neurophysiological model of human wetness sensitivity has been developed. In helping clarifying the peripheral and central neural mechanisms involved in sensing skin wetness, this model has provided evidence for the existence of a specific human hygrosensation strategy, which is underpinned by perceptual learning via sensory experience. Remarkably, this strategy seems to be shared by other hygroreceptor-lacking animals. However, questions remain on whether these sensory mechanisms are underpinned by specific neuromolecular pathways in humans. Although the first study on human wetness perception dates back to more than 100 years, it is surprising that the neurophysiological bases of such an important sensory feature have only recently started to be unveiled. Hence, to provide an overview of the current knowledge on human hygrosensation, along with potential directions for future research, this review will examine the psychophysical and neurophysiological bases of human skin wetness perception.

Neurophysiology of Skin Thermal Sensations

“…As the psychophysics of skin wetness perception have been recently reviewed in details elsewhere (see (101), these will only briefly be outlined below.…”

“…we learn to associate the sensations experienced when in contact with moisture to the actual perception of skin wetness). It could be argued that in the absence of a specific hygroreceptors, humans have learnt to associate the experience of wetness to secondary sensory inputs (thermal and tactile), by retaining a neural representation of a "typical wet stimulus" (98,101) which is generated and shaped by repeated sensory experiences (i.e. exposures to wet stimuli).…”

“…mechanical pressure and skin friction) inputs, as generated the interaction between skin, moisture and (if donned) clothing (109), could be used to determine the presence and degree of skin wetness, through a complex multisensory integration (89), which is shaped and refined by repeated exposures to the same wet stimuli. In this context, skin thermal and tactile sensitivities seem therefore to play an important role in the ability to sense skin wetness (101).…”

Human wetness perception of fabrics under dynamic skin contact

“…The neurophysiological basis of wetness perception has been well documented in the classical work conducted by Bentley (1900), and has seen a revival in the last decade (Bergmann Tiest et al 2012;Filingeri and Havenith 2015). However, in order to improve moisture sensation and thermal comfort of clothing it would be of great value to identify the textile parameters that trigger cutaneous thermal and mechanical inputs underpinning wetness perception.…”

“…The human ability to perceive skin wetness causes tactile and thermal discomfort (Fukazawa and Havenith 2009), this driving behavioural thermoregulatory responses (Schlader et al 2010) aimed at maintaining homeostasis, ensuring health and survival (Parsons 2002). In absence of visual or auditory cues, skin wetness is perceived via learning processes (Bentley 1900) and through the central integration of thermal and mechanical stimuli occurring at the skin (Bergmann Tiest et al 2012;Filingeri and Havenith 2015).…”