Hyperthermia, but not dehydration, alters the electrical activity of the brain
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ORIGINAL ARTICLE
Hyperthermia, but not dehydration, alters the electrical activity of the brain Anne M. J. van den Heuvel1 · Benjamin J. Haberley1 · David J. R. Hoyle1 · Nigel A. S. Taylor1,2 · Rodney J. Croft2 Received: 4 March 2020 / Accepted: 3 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Whole-body thermal and hydration clamps were used to evaluate their independent and combined impact on the electrical activity of the brain. It was hypothesised that those stresses would independently modify the electroencephalographic (EEG) responses, with those changes being greater when both stresses were superimposed. Methods Alpha and beta spectral data (eyes closed) were collected from the frontal, central-parietal and occipital cortices of both hemispheres in resting, healthy and habitually active males (N = 8; mean age 25 years). Three dehydration states were investigated (euhydrated and 3% and 5% mass decrements) in each of two thermal states (normothermia [mean body temperature 36.3 °C] and moderate hyperthermia [38.4 °C]). The combination of those passively induced states yielded six levels of physiological strain, with the EEG data from each level separately examined using repeated-measures ANOVA with planned contrasts. Results When averaged across the frontal cortices, alpha power was elevated relative to the occipital cortices during moderate hyperthermia (P = 0.049). Conversely, beta power was generally reduced during hyperthermia (P = 0.013). Neither the alpha nor beta power spectra responded to dehydration, nor did dehydration elevate the heat-induced responses (P > 0.05). Conclusion Moderate hyperthermia, but neither mild nor moderate dehydration, appeared to independently alter brain electrical activity. Moreover, the combination of moderate hyperthermia with 5% dehydration did not further increase those changes. That outcome was interpreted to mean that, when those states were superimposed, the resulting neurophysiological changes could almost exclusively be attributed to the thermal impact per se, rather than to their combined influences. Keywords Brain electrical activity · Dehydration · Electroencephalogram · Heat strain · Hyperthermia Abbreviations EEG Electroencephalographic EOG Electro-oculographic E1, E3, E5 and E6 Electrode positions above and below the left eye, and at the outer canthi of the left and right eyes (respectively)
Communicated by George Havenith. * Nigel A. S. Taylor [email protected] 1
Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW 2522, Australia
Australian Centre for Electromagnetic Bioeffects Research, School of Psychology, Illawarra Health & Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia
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Introduction This communication comes from a large, multi-disciplinary investigation in which the independent and combined influences of dehydration (hypohydration) and moderate hyperthermia were explored using hydration and th
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