Acute Whole-Body Heat Exposure Modulates EEG Microstate Dynamics, Phase-Lagged Connectivity, and Cortical Source Activity

Abstract Acute exposure to elevated ambient temperature affects physiological regulation, thermal perception, and cognitive functioning, yet its influence on the spatiotemporal organization of human brain activity remains insufficiently understood. This study investigated temperature-related changes in EEG spectral power, microstates, functional connectivity, and cortical source activity. Fifteen healthy male participants completed three randomized 45-min seated exposures at ambient temperatures of 21, 30, and 38 °C while wearing standardized winter protective clothing (3.2 clo). EEG, skin temperature, core body temperature, and subjective thermal sensation were recorded. Mean skin temperature, core body temperature, and thermal-sensation votes increased with temperature and exposure duration. Global delta-band connectivity differed significantly across temperatures (χ 2 =12.64, FDR-adjusted q=0.0090). Delta connectivity was significantly higher at 38 °C than at 21 °C. Microstate D coverage differed across temperatures, with values of 0.145, 0.178, and 0.150 at 21, 30, and 38 °C, respectively (χ 2 =12.88, FDR-adjusted q=0.0064, W=0.429). Source-space analysis further demonstrated increased relative delta source power with temperature and reduced beta and gamma source power at 38 °C, particularly in occipital, parietal, sensorimotor, and posterior cingulate regions. Increasing ambient temperature was associated with a shift in EEG spectral activity toward lower frequencies, enhanced delta-band functional synchronization, and altered microstate temporal organization. Together, these exploratory findings indicate that spectral power, regional phase-lagged connectivity, and microstate dynamics show distinct responses to ambient temperature in healthy young men wearing protective clothing.