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Researchers at University of Tsukuba report that a regular regimen of light-intensity exercise, such as slow running, facilitates the extinction of contextual fear memories—a key experimental model for studying post-traumatic stress disorder (PTSD)—in rats. Building on the team's longstanding work, the study links this effect to reduced neural activity in hippocampal regions involved in fear memory recall and anxiety.

Tsukuba, Japan—Exercise has gained attention as a promising nonpharmacological intervention for stress-related disorders such as PTSD. However, moderate- to vigorous-intensity exercise may impose physical and psychological demands, limiting its accessibility for individuals with heightened stress sensitivity. In response to this challenge, the research team focused on light-intensity exercise, such as yoga and slow running, which may be more accessible. Using a rat model, they showed that a regular regimen of light-intensity running promotes the extinction of contextual fear memories, an experimental model relevant to PTSD-related fear (Shimoda and Soya et al., Med Sci Sports Exerc, 2024).

The present study builds on the team's previous work, which showed that light-intensity running influences hippocampal function by increasing brain-derived neurotrophic factor expression and promoting neurogenesis, two processes that support neuroplasticity and facilitate fear memory extinction. Recent studies suggest that these forms of neuroplasticity suppress hippocampal circuits involved in fear memory recall (i.e., the retrieval of fear memories). Based on this evidence, the researchers hypothesized that a similar inhibitory mechanism might underlie the effects of regular light-intensity running.

To test this hypothesis, the study evaluated brain activity in rats that underwent fear conditioning followed by four weeks of light-intensity running. The results exhibited reduced neural activity during fear extinction learning in the dorsal CA3 region of the hippocampus, a region critically involved in fear responses that plays an important role in fear memory recall. Neural activity in this region positively correlated with fear response intensity, indicating that lower dorsal CA3 activity was associated with weaker fear responses. Additionally, neuronal activity in the ventral dentate gyrus, which is involved in anxiety expression, was also reduced.

The researchers propose that the facilitation of fear memory extinction by regular light-intensity running is associated with reduced neural activity in the dorsal CA3 region of the hippocampus and the ventral dentate gyrus. Together with the team's previous findings, these results provide a more integrated understanding of how regular light-intensity exercise promotes adaptive hippocampal plasticity and fear extinction. These findings support light-intensity exercise as an accessible and effective nonpharmacological intervention for individuals with PTSD who have difficulty performing moderate- to vigorous-intensity exercise.

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This research was supported in part by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research (A) (18H04081, 21H04858, and 24H00670) (to H.S.), by The Ministry of Education, Culture, Sports, Science and Technology (MEXT)/JSPS KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas: Next Generation Exercise Program for Developing Motivation, Body and Mind Performance (16H06405) (to H.S.), and by the Japan Science and Technology Agency (JST)-Mirai Program (JPMJMI19D5) (to H.S.).

Original Paper

Title of original paper:

Regular light-intensity exercise accelerates contextual fear extinction with reduced dorsal CA3 activation in male rats

Journal:

Neurochemistry International

DOI:

10.1016/j.neuint.2026.106191

Correspondence

Visiting Professor SOYA Hideaki
Center for Cybernics Research, University of Tsukuba
Professor Emeritus, Institute of Health and Sport Sciences, University of Tsukuba

Related Link

Center for Cybernics Research

Institute of Health and Sport Sciences