Regular light-intensity exercise erases fear memory — Findings from the University of Tsukuba expected to aid in PTSD prevention

On August 29, a research group led by Professor Hideaki Soya of the Institute of Health and Sport Sciences at the University of Tsukuba has announced that regular light-intensity exercise promotes the extinction of fear memory, and that brain-derived neurotrophic factor (BDNF) is involved as a neuromolecular basis for this process. The findings are expected to contribute to the development of new exercise-based PTSD treatment and prevention programs. The results were published in the international journal Medicine & Science in Sports & Exercise.

Post-traumatic stress disorder (PTSD) is one of the most common stress-induced mental disorders, and exercise has recently been reported to be effective in its prevention and treatment. Common treatments involve cognitive behavioral therapy to help the patients reconceptualize the original traumatic memory as "not scary." The hippocampus, which controls memory and learning, plays a major role in this process, and one of the molecules responsible for this neural basis is hippocampal BDNF. Administration of BDNF to the limbic system region, including the hippocampus, has been found to promote fear memory extinction through relearning.

Previously, the research group reported that very light, low-intensity exercise activated the hippocampus and enhanced BDNF expression and memory learning. In the present study, they investigated whether low-intensity exercise is also effective in extinguishing fear memory and whether BDNF is involved.

In the experiment, rats were placed in a box, given mild electrical stimuli as fear memory, removed from the box, and given low-intensity exercise training for four weeks. Then, the rats were placed back in the box to observe their behavior, which was compared with that of rats that received no exercise training.

When rats are fearful, they exhibit freezing behavior. All rats showed freezing behavior in the beginning, but the rats that exercised gradually became more active. Regardless of the exercise intensity, the fear memory was updated and extinguished more quickly in the rats with exercise than in the sedentary condition group. Furthermore, administration of a BDNF inhibitor to rats after low-intensity exercise abolished the effects of exercise. This result indicates that BDNF signaling is involved in the extinction of fear memory.

Soya said, "PTSD can develop when we experience strong stress, causing insomnia, depression, feelings of worthlessness, and fear. Prolonged PTSD symptoms can inhibit wellbeing. However, light-intensity exercise just for four weeks after stress was found to mitigate stress symptoms through BDNF action in the hippocampus. This exercise therapy has been shown to promote neurogenesis and memory capacity in the hippocampus. Light-intensity exercise (therapy) has the power to improve mental health by enhancing hippocampal function."