title: Cooling reduces the cutaneous afferent firing response to vibratory stimuli in glabrous skin of the human foot sole.
abstract: Skin on the foot sole plays an important role in postural control. Cooling the skin of the foot is often used to induce anesthesia to determine the role of skin in motor and balance control. The effect of cooling on the four classes of mechanoreceptor in the skin is largely unknown, and thus the aim of the present study was to characterize the effects of cooling on individual skin receptors in the foot sole. Such insight will better isolate individual receptor contributions to balance control. Using microneurography, we recorded 39 single nerve afferents innervating mechanoreceptors in the skin of the foot sole in humans. Afferents were identified as fast-adapting (FA) or slowly adapting (SA) type I or II (FA I n = 16, FA II n = 7, SA I n = 6, SA II n = 11). Receptor response to vibration was compared before and after cooling of the receptive field (2-20 min). Overall, firing response was abolished in 30% of all receptors, and this was equally distributed across receptor type (P = 0.69). Longer cooling times were more likely to reduce firing response below 50% of baseline; however, some afferent responses were abolished with shorter cooling times (2-5 min). Skin temperature was not a reliable indicator of the level of receptor activation and often became uncoupled from receptor response levels, suggesting caution in the use of this parameter as an indicator of anesthesia. When cooled, receptors preferentially coded lower frequencies in response to vibration. In response to a sustained indentation, SA receptors responded more like FA receptors, primarily coding "on-off" events.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Catherine R
authors.initials: CR
authors.lastname: Lowrey
authors.forename: Nicholas D J
authors.initials: ND
authors.lastname: Strzalkowski
authors.forename: Leah R
authors.initials: LR
authors.lastname: Bent
mesh_terms: D000200:Action Potentials; D000222:Adaptation, Physiological; D000328:Adult; D003080:Cold Temperature; D005260:Female; D005545:Forefoot, Human / Q000294:innervation*; D006801:Humans; D008297:Male; D008465:Mechanoreceptors / Q000145:classification / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology; D012867:Skin / Q000166:cytology / Q000294:innervation*; D014110:Touch; D014732:Vibration