Hyperthermia-Induced Changes in EEG of Anesthetized Mice Subjected to Passive Heat Exposure

Abstract

Currently, the role of hypothermia in electroencephalography (EEG) is well-established. However, few studies have investigated the effect of hyperthermia on EEG, an important physiological parameter governing brain function. The aim of this work was to determine how neuronal activity in anesthetized mice is affected when the temperature rises above the physiological threshold mandatory to maintain the normal body functions. In this study, a temperature-elevation protocol, from 37 to 42°C, was applied to four female mice of 2-3 months old while EEG was recorded simultaneously. We found that hyperthermia reduces EEG amplitude by 4.36% when rising from 37 to 38 degrees and by 24.33% when it is increased to 42 degrees. Likewise, increasing the body temperature produces a very large impact on the EEG spectral parameters, reducing the frequency power at the delta, theta, alpha, and beta bands. Our results show that hyperthermia has a global effect on the EEG, being able to change the electrical activity of the brain.

Keywords: anesthetized animal; electroencephalography; hyperthermia; mice; physiology.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 de Labra, Pardo-Vazquez, Cudeiro and Rivadulla.

Figures

FIGURE 1

Recording setup. (A) Experimental preparation. Anesthetized mice were placed under a heat lamp while the core temperature was monitored and the EEG recorded. (B) Protocol for increasing the mice’s temperature.

FIGURE 2

Example EEG signal and spectrogram at 37°C. (A) Sixty-second segment of the EEG signal. (B) One-second recording expanded from panel (A). (C,D) Spectrograms of the EEG signals in panels (A,B), respectively.

FIGURE 3

Changes in the EEG as a function of the core temperature recorded from two different mice. (A,C) Raw EEG data (black trace, left y-axis) and core temperature (red trace, right y-axis). (B,D) Details from the recordings depicted in panels (A,C), respectively, showing 20 s during which the temperature of the mouse was 37°C (left panels) and 42°C (right panels).

FIGURE 4

The amplitude of the EEG decreases as the temperature increases. (A) Maximum amplitude of the normalized EEG signal within each 5-s epoch (averaged across epochs) as a function of core temperature, for one example recording session. (B) Mean and SD (black dots) and individual values for each 5-s epoch (gray dots) comparing the maximum amplitude between 37 and 42°C for the same session. (C) The same as in panel (A), but averaged across sessions (n = 19). (D) The same as in panel (B) but averaged across recording sessions (gray dots for individual sessions, n = 19).

FIGURE 5

The effect of the temperature on the EEG is due to changes in the delta, theta, alpha and beta bands. (A) Power spectra for different frequency bands for each individual recording session, normalized between 0 and 1 and averaged across 5-s bins (thin lines) and averaged across sessions (thick lines). (B) Power averaged across frequencies of the spectra in panel (A). Gray dots represent individual sessions (n = 19), and black dots represent the average across sessions (mean ± SD). *p < 0.01; **p < 0.005; ***p < 0.0001.