Exercise-induced Dehydration Alters Brain Activation During A Cognitive-motor Task

Abstract

Exercise-induced dehydration decreases endurance performance in the heat; but effects on cognitive function appear equivocal. Brain activation may be greater during executive function tasks following dehydration, indicating greater mental resources are needed to maintain performance. PURPOSE: To examine if, following exercise-induced dehydration, low level cognitive motor tasks (i.e. fine motor pacing) are impacted along with alterations in brain activity. METHODS: Four physically-active adults (2 male, 2 female; 27.5 ± 13.7 y) completed three experimental sessions: control (no exercise; CON), dehydration induced by 3 h walk/rest cycles (45 min on, 15 min rest) in a hot environment (45°C, 15% RH) (DEH), and matched intermittent walking in the heat with fluid consumed to match sweat loss (EUH). Using functional magnetic resonance imaging (fMRI), blood oxygen level dependent (BOLD) responses were recorded while subjects performed a visually paced (1 Hz) cognitive motor task with the right index finger. RESULTS: Mean change in % body mass was significantly greater for DEH (−3.2 ± 0.5%) compared to EUH (−0.2 ± 0.2 %; p 0.05), as was reaction time (CON: 91.1 ± 22.9, EUH: 113.3 ± 9.7, DEH: 118.0 ± 37.4 ms; p > 0.05). Comparison of neural activations from DEH vs. EUH and DEH vs. CON revealed significantly greater (Z = 1.6, p < 0.05; cluster corrected for multiple comparisons) activity in bilateral cerebellum as well as bilateral visual cortex, left inferior and superior parietal lobe, and left sensorimotor cortex. No differences in neural activation were observed for EUH versus CON. CONCLUSIONS: Significantly heightened brain activation was associated with DEH compared to both control and exercise in the heat while maintaining hydration despite no change in cognitive motor performance. This suggests neural inefficiencies due to dehydration present in low level cognitive motor tasks are not isolated to higher level executive function tasks. Supported by a grant from Center for Advanced Brain Imaging, Georgia Institute of Technology, Atlanta, GA