Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Jacob F Piil,Leonidas G Ioannou,Jesper Lundbye-Jensen,Lasse Christiansen,Andreas D Flouris,Lars Nybo,C Jacob Mikkelsen,Nathan B Morris

doi:10.1038/s41598-020-64768-w

Abstract

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m2). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. Importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects.

Highlights

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming
To separate the effects of heating the head from general body core hyperthermia, we used the interval between early peaks of the brainstem auditory evoked potentials (BAEPs), as this measurement is a sensitive marker for deep brain temperature changes[18,22]
The present study provides proof-of-principle that prolonged radiant heat exposure of the head impairs motor-cognitive performance, with small but significant impairments in the simple motor task performance and large performance decrements in the complex motor and combined motor-cognitive task

Summary

Introduction

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Negative effects range from thermal discomfort and impaired physical work capacity for healthy adults[3] to increased morbidity for workers regularly experiencing hyperthermia[1] and higher mortality for vulnerable citizens during heat-waves[4,5] While these issues are well-documented and exposure likely to be worsened by global warming, the effect of environmental heat stress on performance in cognitively dominated tasks is less clear. The present study investigated how direct exposure of the head to simulated solar radiation, compared to solar radiation applied to the lower-body, affected motor-cognitive task performance and markers of deep brainstem temperature changes. We hypothesized that direct solar exposure to the head would impair performance in the combined motor-cognitive test battery, either by heating the entire brain or via effects confined to cortical areas

Methods

Results

Conclusion