Thermal and tactile interactions in the perception of local skin wetness at rest and during exercise in thermo-neutral and warm environments

Abstract

Abstract AbstractThe central integration of thermal (i.e. cold) and mechanical (i.e. pressure) sensory afferents is suggested as to underpin the perception of skin wetness. However, the role of temperature and mechanical inputs, and their interaction, is still unclear. Also, it is unknown whether this intra-sensory interaction changes according to the activity performed or the environmental conditions. Hence, we investigated the role of peripheral cold afferents, and their interaction with tactile afferents, in the perception of local skin wetness during rest and exercise in thermo-neutral and warm environments. Six cold-dry stimuli, characterised by decreasing temperatures [i.e. -4, -8 and -15°C below the local skin temperature (Tsk)] and by different mechanical pressures [i.e. low pressure (LP): 7 kPa; high pressure (HP): 10 kPa], were applied on the back of 8 female participants (age 21 ± 1 years), while they were resting or cycling in 22 or 33°C ambient temperature. Mean and local Tsk, thermal and wetness perceptions were recorded during the tests. Cold-dry stimuli produced drops in Tsk with cooling rates in a range of 0.06 to 0.4°C/s. Colder stimuli resulted in increasing 4 coldness and in stimuli being significantly more often perceived as wet, particularly when producing skin cooling rates of 0.18°C/s and 0.35°C/s. However, when stimuli were applied with HP, local wetness perceptions were significantly attenuated.Wetter perceptions were recorded during exercise in the warm environment. We conclude that thermal inputs from peripheral cutaneous afferents are critical in characterizing the perception of local skin wetness. However, the role of these inputs might be modulated by an intra-sensory interaction with the tactile afferents. These findings indicate that human sensory integration is remarkably multimodal.Keywords: Keywords: Keywords: Keywords: skin wetness; thermo-receptors; mechano-receptors; sensory integration; perception 5The perception of skin wetness is a complex somatosensory experience which seems to result from the intra-sensory integration of temperature and mechanical inputs (Ackerley et al. 2012;Bergmann Tiest et al. 2012;Bentley, 1900). Although humidity-receptors have been previously described in some insects (Yokohari and Tateda, 1976), these receptors have not been identified in human skin (Clark and Edholm, 1985). It is currently suggested that as human beings, we "learn" to perceive the wetness experienced when our skin is in contact with a wet surface, when a liquid is touched, or when sweat is produced (Bergmann Tiest et al. 2012) through a complex multisensory integration (Driver and Spence, 2000;Gescheider and Wright, 2012). The physical processes which occur when the skin is in contact with moisture (i.e. heat transfer and mechanical interactions between the skin and the environment) generate thermal and mechanical inputs which could be integrated and combined at different anatomical levels through specific multisensory pathways (Cappe et al. 2009). Hence, it ...

Neurophysiology of Skin Thermal Sensations

“…temperature range: 4 to 15°C lower than local skin temperature; area of stimulation: 25 cm 2 ) were applied with a higher (10 KPa) than with a lower (7 KPa) static pressure. This, despite both high and low pressure stimuli induced similar drops in skin temperature (103).…”

“…This simple observation has led to a number of investigations exploring how other somatosensory stimuli (e.g. mechanical and tactile) could therefore contribute to the perception of skin wetness in the absence of cold sensations (16,98,103). As a result of such studies, evidence has emerged in support of the fact that when thermal cues are insufficient, individuals seems to rely on mechanical and tactile inputs (e.g.…”

“…stickiness) to sense skin wetness. This is particularly true under conditions of sweat-induced skin wetness (16,98,103). For example, under conditions of sweat-induced skin wetness, and especially when wearing clothing, skin wetness perception has been shown to be driven primarily by tactile stimuli in the form of intermittent mechanical interaction between skin, sweat and clothing (100,109,120,191).…”

“…This has been recently demonstrated in one of this author' study (100), in which the alteration of the interactions skin-sweat-clothing under conditions of sweat-induced skin wetness, significantly modulated the perception of skin wetness, independently of the level of physical skin wetness. Finally, in light of this neural model, perceptual illusions such as the one where skin wetness is experienced as a result of cold-dry stimulation (102,103), could be explained and interpreted as the result of a sensory system which relies on rational integration mechanisms which are based on specific sensory inputs (e.g. coldness), and which are selectively used to characterize a specific sensory experience.…”

“…The synthetic nature of wetness is highlighted by the simple, but powerful observation that in the presence of specific thermal and tactile sensory inputs, wetness can be experienced, regardless of whether the inputs are produced by actual contact with moisture stimuli (e.g. see contact with col-dry stimuli) (102,103). Similarly, in the absence of these specific sensory inputs (e.g.…”