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Cold sensations are suggested as the primary inducer of the perception of skin wetness.However, limited data are available on the effects of skin cooling. Hence, we investigated the role of peripheral cold afferents in the perception of wetness. Six cold-dry stimuli (producing skin cooling rates in a range of 0.02 to 0.41°C/s) were applied on the forearm of 9 female participants.Skin temperature and conductance, thermal and wetness perception were recorded. Five out of 9 participants perceived wetness as a result of cold-dry stimuli with cooling rates in a range of 0.14 to 0.41°C/s, while 4 did not perceive skin wetness at all. Although skin cooling and cold sensations play a role in evoking the perception of wetness, these are not always of a primary importance and other sensory modalities (i.e. touch and vision), as well as the inter-individual variability in thermal sensitivity, might be equally determinant in characterising this perception.

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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 ...

Regional differences in thermal sensation to a hot or cold stimulus are often limited to male participants, in a rested state and cover minimal locations. Therefore, magnitude sensation to both a hot and cold stimulus were investigated during rest and exercise in 8 females (age: 20.4 ± 1.4 years, mass: 61.7 ± 4.0 kg, height: 166.9 ± 5.4 cm, VO2max: 36.8 ± 4.5 ml·kg(-1)·min(-1)). Using a repeated measures cross over design, participants rested in a stable environment (22.3 ± 0.9°C, 37.7 ± 5.5% RH) whilst a thermal probe (25 cm(2)), set at either 40°C or 20°C, was applied in a balanced order to 29 locations across the body. Participants reported their thermal sensation after 10s of application. Following this, participants cycled at 50% VO2max for 20 min and then 30% VO2max whilst the sensitivity test was repeated. Females experienced significantly stronger magnitude sensations to the cold than the hot stimulus (5.5 ± 1.7 and 4.3 ± 1.3, p<0.05, respectively). A significant effect of location was found during the cold stimulation (p<0.05). Thermal sensation was greatest at the head then the torso and declined towards the extremities. No significant effect of location was found in response to the hot stimulation and the pattern across the body was more homogenous. In comparison to rest, exercise caused a significant overall reduction in thermal sensation (5.2 ± 1.5 and 4.6 ± 1.7, respectively, p<0.05). Body maps were produced for both stimuli during rest and exercise, which highlight sensitive areas across the body.

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Thermoregulatory parameters during exercise are typically reported as global responses (Tcore and mean Tsk). In contrast, this study investigated regional skin temperatures (Tsk) over the body, in relation to regional skinfold thickness and regional perceptual responses for both sexes using a body-mapping approach. Nine males and nine females, of equivalent fitness, minimally clothed, ran for 40 minutes at 70% VO2max in a 10°C, 50% rh, 2.8 m.s-1 air velocity environment. Tsk was recorded by infrared thermography and processed to obtain population-averaged body maps. Rectal temperature and heart rate were monitored continuously throughout the running trial. Skinfold thickness was obtained for 24 sites and thermal sensation votes for 11 body regions. Males and females had similar rectal temperature, heart rate and regional sensations. Whole-body maps of Tsk highlighted the significantly lower regional Tsk for females (-1.6°C overall, p<0.01). However, the distribution of Tsk across the body was similar between sexes and this was not correlated with the distribution of skinfold thickness, except for the anterior torso. On the other hand, regional thermal sensation votes across the body were correlated with Tsk distribution during exercise (females: r = 0.61, males r = 0.73, p<0.05), but not at rest. Our thermographic results demonstrate the similar Tsk distribution for active males and females during submaximal running in the cold, though shifted to a lower mean value for females. This Tsk distribution was associated with regional sensations but not with local fat thickness. The described body-mapping approach can have implications in physiological modelling and clothing design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 and heart rate were monitored continuously throughout the running trial. Skinfold thickness was 9 obtained for 24 sites and thermal sensation votes for 11 body regions. 10Males and females had similar rectal temperature, heart rate and regional sensations. Whole-body 11 maps of T sk highlighted the significantly lower regional T sk for females (-1.6°C overall, p<0.01). 12However, the distribution of T sk across the body was similar between sexes and this was not correlated

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