The effects of thermal strain on cognition

Abstract

Military operations in tropical environments have imposed a significant challenge to the Australian Defence Force (ADF). The hot and humid conditions are known to cause debilitating effects on soldiers deployed to northern regions of Australia, with the consequence that the effectiveness and efficiency of operations were severely compromised. While the adverse effects of thermal stress on soldiers' physiological capability are well established, this has not been confirmed for cognitive performance. This impact of thermal strain on cognition has now been studied using psychometric testing and functional brain electrical activity imaging to investigate the impact of thermal stress on cognitive performance. The brain electrical activity of subjects was measured while undertaking a range of cognitive tasks. Steady State Probe Topography (SSPT), a novel brain imaging technology, was employed to monitor the changes in regional brain activity and neural processing speed of subjects under thermal stress. The psychometric test batteries, developed by the Brain Sciences Institute (BSI), were made up of the Rey auditory-verballeaming test, the inspection time, the digit span test the spatial working memory task and the AX-continuous performance task The functional brain imaging provides topographical information, which shows changes of electrical activity in response to thermal stress during cognitive task performance. The changes in brain electrical activity and neural speed induced by thermal stress will help to identify the type of cognitive functions that are likely to be impaired. Results indicated that subjects experienced increasing cardiovascular strain through thermally neutral to thermally straining conditions. The heat strain imposed on the subjects was substantial as indicated by the increase in their mean core temperature under thermally straining conditions. The psychometric test batteries, however, showed no significant performance decrements even under the most strenuous condition. Some deficits in working memory, in information retention and processing were noted but overall, behavioural changes that were reflective of the higher level of thermal strain were not observed. In contrast, there were marked differences in the electrical responses of the brain when subjects were thermally strained. The Steady State Visual Evoked Potential (SSVEP) recordings showed an increase in amplitude and a decrease in latency, suggesting an increase in the utilisation of neural resources or effort by subjects to maintain the same level of performance under thermally neutral conditions. It appears that the brain imaging technology is potentially a valuable tool for examining the empirical relationships that complements and goes beyond conventional measures of behavioural responses.