Warm hands, cold heart: progressive whole-body cooling increases warm thermosensitivity of human hands and feet in a dose-dependent fashion

While inhibitory/facilitatory central modulation of vision and pain has been investigated, contextual modulation of skin temperature integration has been unexplored. Hence, we tested whether progressive decreases in whole-body mean skin temperature (Tsk) (a large conditioning stimulus) alter the magnitude estimation of local warming and cooling stimuli applied to hairy and glabrous skin. On 4 separate occasions, 8 males (27 ± 5y) underwent a 30-min whole-body cooling protocol (water-perfused-suit; temperature: 5 C), during which a quantitative thermosensory test, consisting of reporting perceived magnitude of warming and cooling stimuli (±8°C from 30°C baseline) applied to the hand (palm/dorsum) and foot (sole/dorsum), was performed before cooling and every 10 min thereafter. The cooling protocol resulted in large progressive reductions in whole-body Tsk (10 min: -3.36 C (95% CI: -2.62, -4.10); 20 min: −5.21°C (−4.47, -5.95); 30 min: −6.32°C ( −5.58, -7.05); P < 0.001), with minimal changes (∼0.08 C) in rectal temperature. While thermosensitivity to local skin cooling remained unchanged (P = 0.831), sensitivity to skin warming increased significantly at each level of whole-body Tsk for all skin regions (10 min: +4.9% (−1.1, +11.0); 20 min: +6.1% (+0.1, 12.2); 30 min: +7.9% (+1.9, +13.9); P = 0.009). Linear regression indicated a 1.2%.°C−1 increase in warm thermosensitivity with whole-body skin cooling. Overall, large decreases in whole-body Tsk significantly facilitated warm, but not cold, sensory processing of local thermal stimuli, in a dose-dependent fashion. In highlighting a novel feature of human temperature integration, these findings point to the existence of an endogenous thermosensory system that could modulate local skin thermal sensitivity in relation to whole-body thermal states.