Spinal and corticospinal excitability in response to reductions in skin and core temperatures via whole-body cooling

Cold stress impairs fine and gross motor movements. Although peripheral effects of muscle cooling on performance are well understood, less is known about central mechanisms. This study characterized corticospinal and spinal excitability during surface cooling, reducing skin (T_sk) and esophageal (T_es) temperatures. Ten subjects (3 females) wore a liquid-perfused suit and were cooled (9 °C perfusate, 90 min) and rewarmed (41 °C perfusate, 30 min). Transcranial magnetic stimulation (eliciting motor evoked potentials [MEPs]), as well as transmastoid (eliciting cervicomedullary evoked potentials [CMEPs]) and brachial plexus (eliciting maximal compound motor action potentials [M_max]) electrical stimulation, were applied at baseline, every 20 min during cooling, and following rewarming. Sixty minutes of cooling reduced T_sk by 9.6 °C (P < 0.001), but T_es remained unchanged (P = 0.92). T_es then decreased by ∼0.6 °C in the next 30 min of cooling (P < 0.001). Eight subjects shivered. During rewarming, shivering was abolished, and T_sk returned to baseline, while T_es did not increase. During cooling and rewarming, M_max, MEP, and MEP/M_max remained unchanged from baseline. However, CMEP and CMEP/M_max increased during cooling by ∼85% and 79% (P < 0.001), respectively, and remained elevated post-rewarming. The results suggest that spinal excitability is facilitated by reduced T_sk during cooling and reduced T_es during warming, while corticospinal excitability remains unchanged. ClinicalTrials.gov ID: NCT04253730. Novelty: This is the first study to characterize corticospinal and spinal excitability during whole-body cooling and rewarming in humans. Whole body cooling did not affect corticospinal excitability. Spinal excitability was facilitated during reductions in both skin and core temperatures.