Key to stress adaptation found "1 hour later": Brain activity peak timing revealed

A research group including Kochi University of Technology has revealed that brain activity for adapting to intense stress peaks not immediately after the stress, but approximately one hour later. This finding reportedly overturns the conventional theory that "the brain's stress response peaks within 30 minutes." Advancing this research further is expected to lead to effective stress management strategies in mental healthcare and during education.

Even when experiencing similar stress, some individuals adapt immediately, recover, and lead healthy lives, while others struggle to adapt and take longer to recover. A research group including Associate Professor Noriya Watanabe of the Faculty of Informatics at Shizuoka Institute of Science and Technology, who is conducting research on affective neuroscience, and Professor Masaki Takeda, Director of the Research Center for Brain Communication at Kochi University of Technology (neuroscience/AI), sought to investigate what brain mechanisms underlie these individual differences. Long-term stress is known to potentially trigger PTSD (Post-Traumatic Stress Disorder) and depression, and clarifying the intracerebral mechanisms involved in adapting to stress could aid in treatment.

In this study, 102 students enrolled at Kochi University of Technology and its graduate school completed a 25-item questionnaire on a 5-point scale to assess the strength of their stress adaptability. The experiment was conducted on 90 participants aged 18 to 25 (68 males, 22 females) whose responses were consistent.

The experiment was conducted by arranging a classical physical stress loading method called the "cold pressor test". Participants wore a glove for 2 minutes that induced a cold sensation equivalent to submerging a hand in ice water. In addition to measuring physiological changes such as heart rate and stress hormone levels before and after the test, the researchers examined brain activity using fMRI (functional Magnetic Resonance Imaging) and EEG (electroencephalography).

Imaging of the brain immediately after, 20 minutes after, 60 minutes after, and 80 minutes after the stress showed that on fMRI scans, individuals with higher stress adaptability exhibited a clear calming of activity in the "salience network," which governs stress responses and tension, at the 60-minute mark. Concurrently, activity in the "default mode network," which activates during introspection and rest, was strengthened. Looking at the EEG data, waves associated with states of tension dropped significantly at 60 minutes. Conversely, the opposite reactions occurred in individuals with weak stress adaptability. No significant differences were observed immediately after or 20 minutes after the stress.

When subjected to some form of stress, bodily responses such as pupil dilation, heart racing, and the secretion of stress hormones have conventionally been understood to peak 30 minutes after exposure and return to the baseline by 60 minutes. However, this experiment revealed that brain activity involved in stress adaptation peaks approximately 60 minutes after exposure and continues to remain active thereafter.

Past brain research regarding stress adaptation frequently relied on inducing depression-like states in mice to examine brain activity. Watanabe noted, "Experiments on mice alone have a limitation in that they cannot directly verify the human-specific 'ability to overcome stress.' In this study, we succeeded in detecting human brain activity related to stress adaptation." Moving forward, he hopes to advance research into these brain mechanisms and explore specific ways to intervene to help individuals adapt to stress.

By conducting 4-hour tests on each of the 90 participants, this study generated a massive volume of data totaling 2 terabytes (tera representing 10¹²). Takeda explained, "It would be wonderful to advance research in a way that maximizes the potential of this data. We can look forward to research that goes beyond just using AI for data analysis. For instance, since studies utilizing generative AI to analyze EEG patterns already exist, I would like to work on developing a system that can provide advice on adjusting stress loads by comparing EEG data from before and after stress exposure."

The study was conducted with support from the Grants-in-Aid for Scientific Research (KAKENHI) by the Japan Society for the Promotion of Science, the Takeda Science Foundation, the Naito Science & Engineering Foundation, and the Public Health Research Foundation. The findings were published on March 26 in the online edition of the Proceedings of the National Academy of Sciences and announced by Kochi University of Technology on the same day.