A Comprehensive Assessment of Physiological and Neural Changes Underlying Cognitive Performance after Heat Stress: A Randomized Clinical Trial.

Heat stress threatens neurological health as a risk factor for cognitive decline. However, deeper understanding of the psychological, cognitive, and neural changes induced by heat stress, with stronger causal inference and biological evidence, is needed. A randomized, crossover, controlled trial was conducted among 30 healthy adults (15 males, 15 females; mean age 21.5 ± 1.5 years) during October-November 2022. Participants were randomly divided into two groups and alternately underwent 2-h exposures to high temperature (32 °C) and moderate temperature (22 °C) at a laboratory in Shanghai, China. Psychological distress was evaluated using a simplified DASS-21 scale. Cognitive function was assessed through neurobehavioral tests (Schulte grid and Stroop tests), with neural activity examined using functional magnetic resonance imaging (fMRI) to assess blood oxygen level-dependent signals. Blood samples were collected for plasma exosome transcriptomics and targeted biomarker analyses. Acute heat exposure significantly increased psychological distress by 27.3%, decreased processing speed by 13.6%, and impaired response inhibition by 3.4%. Heat stress reduced neural activity and synchronization in the precentral gyrus, inferior frontal gyrus, and rostral hippocampus. Functional connectivity was also attenuated in these regions. These alterations might be driven by type I interferon-dominated inflammation, excitotoxicity, and oxidative stress. Conversely, neural regulatory responses were observed, including activation of the lateral occipital cortex and elevated levels of neurotrophic factors. This trial demonstrates the relationship between acute heat exposure and diminished cognitive function. These findings underscore the need for public health strategies to maintain indoor temperatures within a comfortable range and promote active cooling to protect cognitive health.