Exploring cognitive functions variability at ambient temperatures from 20 °C to 48 °C: An fNIRS study

Abstract

Exposure to elevated temperatures is known to impair task performance and diminish work efficiency. Functional near-infrared spectroscopy (fNIRS), celebrated for its non-invasive and portable characteristics, is extensively utilized in brain function research. This study explores the potential of fNIRS signals in assessing cognitive function across a range of ambient temperatures. Twenty-four right-handed university students were subjected to eight temperature conditions (20, 23, 26, 30, 35, 40, 45, and 48 °C) in a climate chamber. Changes in oxygenated hemoglobin (O₂Hb) concentration within the prefrontal cortex (PFC) were measured during both resting and task states using a 22-channel fNIRS system. The data revealed significant variations in brain activity within the lateral prefrontal cortex (VLPFC) and dorsolateral prefrontal cortex (DLPFC) across different temperatures during the resting state. A quadratic relationship (R^2 > 0.7) between ambient temperature and resting state O₂Hb concentrations was established through correlation analysis. Under cognitive tasks, peak activations for the 2-back, trail-making, and addition tests were noted at 20 °C, while the Stroop test reached its peak activation at 26 °C. Further, correlations between task performance and fNIRS-derived cognitive metrics were analyzed. Specifically, the Stroop test displayed pronounced variations in the hemodynamic response function (HRF) relative to ambient temperature, with changes in O₂Hb concentration consistent with variations in task performance as temperatures increased. These findings highlight the reliability of fNIRS as a tool for assessing cognitive dynamics under thermal strain.