Climate change has had a widespread impact on humans and natural systems.  Heat exhaustion is a heat-related illness that can occur after exposure to hot environments.  Signs include excessive thirst, weakness, headache, loss of consciousness, dizziness, muscle cramps, nausea, and vomiting.  Heat exhaustion is not as serious as heat stroke, but without proper intervention, it can progress to heat stroke, which can damage the brain and other vital organs.  The present study focused on the cognitive function and the effect of general treatment for heat exhaustion on the function.  Therefore, we investigated the effects of heat stress (HS) and face/head cooling (FHC) during heat stress on the human cognitive function.

  We used the ‘P300 component’ reflecting neural activity of the human cognitive function, which was recorded using electroencephalography (Figure).  P300 is recorded at about 300 ms after sensory stimulation while performing cognitive tasks.  The P300 amplitude indicates the intensity of neural activity.   Using the Go/No-go paradigms, we investigated the neural activities of motor execution and inhibition.  To create a hot environment, subjects were dressed in a tube-lined water-perfused suit, which can be perfused with hot or cold water.  As the experimental procedure, P300 was recorded at the baseline (Rest) before HS, when the core temperature had increased by ~1.2°C during HS, face/head cooling during HS (FHC), and whole-body cooling (WBC) after HS.  The P300 amplitudes were lower for HS than Rest.  Interestingly, the P300 amplitudes also remained reduced even during FHC.  These results suggest that the cognitive function is reduced during HS, and FHC does not reverse the cognitive impairment caused by the HS.  WBC recovered the executive processing, but the inhibitory processing remained reduced.

　Our results may contribute to the development of a preventative methodology for hyperthermia in daily life and sports activities.

 

Collaborative Researchers

Name: Manabu Shibasaki
Department: Department of Health Sciences, Faculty of Human Life and Environment
Institute: Nara Women’s University

Name: Mari Namba
Department: Graduate School of Humanities and Sciences
Institute: Nara Women’s University

Name: Misaki Oshiro
Department: Graduate School of Humanities and Sciences
Institute: Nara Women’s University

Name: Ryusuke Kakigi
Department: Department of Integrative Physiology
Institute: National Institute for Physiological Sciences

Name: Hiroki Nakata
Department: Department of Health Sciences, Faculty of Human Life and Environment
Institute: Nara Women’s University

Funding

Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (15H02889 to M.S., and 15H05361 to H.N.)