Individual Differences in Cognitive Performance Regulated by Deep-Brain Activity during Mild Passive Hyperthermia and Neck Cooling

Hyperthermia-induced decline in cognitive performance is a moderate complication that poses challenges to the maintenance of safety. Although the underlying mechanism can be attributed to the disruption of brain networks, the propensity remains unclear. This study aimed to test the hypothesis that the extent of the alterations in cognitive performance is governed by the activity of deep brain structures, including monoaminergic neural systems. A decline in cognitive performance during mild hyperthermia and the beneficial effects of neck cooling were demonstrated using the Continuous Performance Test as a battery of cognitive tasks. Aspects of cognitive performance were characterized using the deep-brain activity (DBA) index as a neural activity parameter and the State-Trait Anxiety Inventory to assess the extent of alterations in cognitive performance as an individual measure. It was found that a higher average DBA index during tasks is essential for high cognitive performance in the heat. This beneficial effect of DBA is governed by the upper brainstem. This DBA benefit is more significant for individuals with higher average DBA indices at rest in a normal environment. Individual differences in cognitive performance in the heat are governed by differences in DBA. In addition, the beneficial effect of DBA on cognitive performance in heat only applies under conditions including neck cooling. This limited neck-cooling effect is attributed to anti-homeostatic thermoregulatory responses to cognitive tasks regulated by DBA.