Evaluation of cognitive performance in the heat by functional brain imaging and psychometric testing

Military operations in tropical environments have imposed a significant cha llenge to the Australian Defence Forces (ADF). The hot and humid conditions are known to cause debilitating effects on soldiers deployed to northern r egions of Australia, with the consequence that the effectiveness and effici ency of operations are severely compromised. While the adverse effects of t hermal stress on soldiers' physiological capability are well established, t his has not been confirmed for cognitive performance. A select range of psy chometric tests were administered and functional brain electrical activity imaging was performed to investigate the impact of thermal stress on cognit ive performance. The brain electrical activity of subjects was measured whi le undertaking a range of cognitive tasks. Steady State Probe Topography (S SPT), a novel brain imaging technology, was employed to monitor the changes in regional brain activity and neural processing speed of subjects under t hermal stress. The psychometric test batteries included the following tasks ; Rey Auditory Verbal Learning Test; Inspection Time; Digit Span test; a sp atial working memory task; and the AX-continuous performance task. These ta sks measure a range of cognitive processes including attention, memory, ver bal learning, information processing and concentration. The functional brai n imaging provided topographical information, which showed changes in elect rical activity in response to thermal stress during cognitive performance. These changes in brain electrical activity and neural speed induced by ther mal stress may help to identify the type of cognitive functions that are li kely to be impaired under operational conditions. Results indicated that su bjects experienced increasing cardiovascular strain through thermally neutr al to thermally straining conditions. The results from the psychometric tes t battery showed some promising effects given the small sample size includi ng deficits in working memory, in information retention and in information processing. There was also marked differences in the electrical responses o f the brain when subjects were thermally strained. The Steady-State Visual Evoked Potential recordings showed an increase in amplitude and a decrease in latency, suggesting an increase in the utilisation of neural resources o r effort by subjects to maintain the same level of performance as under the rmally neutral conditions. The data are suggestive of the high sensitivity of brain imaging techniques with high temporal resolution to identify impor tant decrements in cognitive performance in hostile environments. (C) 2001 Elsevier Science Inc. All rights reserved.