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

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/m 2). 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. Approximately half of the global population live in regions where environmental heat stress is an issue that annually affects the ability to live healthy and productive lives 1,2. 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 heatwaves 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. Intriguingly, in laboratory experiments, impairments in cognitively dominated task performance emerge only with profound hyperthermia 6-10 , whereas productivity losses in occupational settings are reported at considerably lower temperatures 1,11. The ability to maintain concentration and avoid attenuation of motor-cognitive performance is certainly of relevance for work and traffic safety as well as for minimizing the risks of making mistakes during other daily tasks. However, the lack of ecological test validity 1,12-14 as well as the low sensitivity of the stereotypical test protocols used in previous clinical or mechanistic studies in controlled indoor settings may have underestimated the impact of environmental heat stress in real-life scenarios 6-10. In particular, although laboratory-controlled environmental heat-stress studies commonly investigate or control for temperature, humidity and wind speed, solar radiation is often neglected, despite contributing a substantial heat load in outdoor settings, especially in the upright position with the human head directly exposed to solar radiation 15. Human brain function is highly dependent on a stable supply of blood glucose and oxygen, but the brain is also highly vulnerable to alterations...

Effect of a Simulated Heat Wave on Physiological Strain and Labour Productivity

“…Although in the near future countries are expected to start moving away from the primary sector of agriculture towards the industries of manufacturing and services, the results of this study could not be generalized to all industrial sectors since they do not reflect what happens in agriculture and construction where solar radiation increases the psychophysical strain experienced by workers [ 7 , 39 ]. Moreover, our study includes healthy young males indicating that different population groups should be examined before generalizing the current findings.…”

Influence of the mode of heating on cerebral blood flow, non‐invasive intracranial pressure and thermal tolerance in humans

“…2016), then an impaired ability to complete complex cognitive tasks (Piil et al . 2017, 2020), and when approaching thermal tolerance, impaired central motor drive, i.e. central fatigue (Caputa et al .…”

Prolonged facemask use in the heat worsens dyspnea without compromising motor-cognitive performance

“…Accordingly, we conducted the present counterbalanced crossover study comparing the effect of mask use compared to a bare-faced control to test whether wearing a facemask would worsen thermal discomfort, perceived dyspnea, thermal physiological responses and impair task performance relying on concentration and motor-cognitive function when measured during (as opposed to days after) heat exposure. In particular, we employed a test battery that has been previously demonstrated to be highly sensitive and reliable for detecting the influence of heat-related factors that affect cognition [12][13][14]. It was hypothesized, based on the self-reported scores [7,10], that mask use would affect cognitively dominated performances and thermal discomfort, but not alter whole-body thermal balance.…”