Neural characterization of the “totonou” state associated with sauna use

Abstract

Saunas are becoming increasingly popular worldwide, being an activity that promotes relaxation and health. Intense feelings of happiness have been reported shortly after enjoying a hot sauna and cold water, what is known in Japan as the "totonou" state. However, no research has investigated what occurs in the brain during the "totonou" state. In the present study, participants underwent a sauna phase, consisting of three sets of alternating hot sauna, cold water, and rest. We elucidated changes in brain activity and mood in the "totonou" state by measuring and comparing brain activity and emotional scales before and after the sauna phase and during the rest phase in each set. We found significant increases in theta and alpha power during rest and after the sauna phase compared to before the sauna phase. Moreover, in an auditory oddball task, the p300 amplitude decreased significantly and MMN amplitude increased significantly after the sauna phase. The increase in MMN indicates higher activation of the pre-attentional auditory process, leading to a decrease in attention-related brain activity P300. Hence, the brain reaches in a more efficient state. Further, the response time in behavioral tasks decreased significantly. In addition, the participants' subjective responses to the questionnaire showed significant changes in physical relaxation and other indicators after being in the sauna. Finally, we developed an artificial intelligence classifier, obtaining an average accuracy of brain state classification of 88.34%. The results have potential for future application.

Influence of Monaural Auditory Stimulation Combined with Music on Brain Activity

“…Interestingly, recent studies indicate that saunas not only facilitate physical relaxation but also significantly increase alpha brain activity [7]. Moreover, our recent research [8] found increased theta and alpha waves after three sauna sessions. Moreover, in the oddball task conducted before and after, there was an increase in mismatch negativity (MMN) amplitude and a reduction in P300 amplitude after the sauna.…”

“…The questionnaire survey consisted of 14 items, extracted from our previous research. These items were chosen because they showed significant changes before and after sauna bathing [8].…”

“…It employs auditory stimuli to generate combination tones, encompassing binaural or monaural beats. These beats span across various frequency domains, such as theta (4-8 Hz), alpha (8)(9)(10)(11)(12)(13), and gamma (30-50 Hz), etc. The primary objective of these auditory stimuli is to elicit a neural frequency following response in the listener [14][15][16].…”