Characteristics of the local cutaneous sensory thermoneutral zone

Skin temperature detection thresholds have been used to measure human cold and warm sensitivity across the temperature continuum. They exhibit a sensory zone within which neither warm nor cold sensations prevail. This zone has been widely assumed to coincide with steady state local skin temperatures between 32-34ᵒC, but its underlying neurophysiology has been rarely investigated. Here we employ two approaches to characterize the properties of sensory thermo-neutrality, testing for each whether neutrality shifts along the temperature continuum depending on adaptation to a preceding thermal state. The focus is on local spots of skin on the palm. Ten participants (30.3±4.8 y) underwent two experiments. Experiment 1 established the cold-to-warm inter-detection-threshold range for the palm’s glabrous skin, and its shift as a function of 3 starting skin temperatures (26, 31 or 36ᵒC). For the same conditions, Experiment 2 determined a thermally neutral zone centered around a thermally neutral point in which thermoreceptors’ activity is balanced. The zone was found to be narrow (~0.98 to ~1.33ᵒC) moving with the starting skin temperature over the temperature span 27.5-34.9ᵒC (Pearson r=33 0.94; p<0.001). It falls within the cold-to-warm inter-threshold range (width: ~2.25 to ~2.47ᵒC) but is only half as wide. These findings provide the first quantitative analysis of the local sensory thermo-neutral zone in humans, indicating that it does not occur only within a specific range of steady-state skin temperatures (i.e. it shifts across the temperature continuum) and that it differs from the inter-detection-threshold range both quantitatively and qualitatively. These findings provide insight into thermoreception neurophysiology.