Exercise stimulates neuron growth and remodels circuits in the hippocampus, disrupting fear-related memory.
- By exercising, neurogenesis, i.e. the process of forming new neurons, is stimulated in the hippocampus.
- This generation of new neurons disrupts fear-related memory and thus allows people to forget the traumatic events that triggered post-traumatic stress syndrome.
- However, neurogenesis and remodeling of hippocampal circuits stimulated by exercise have “less effect on mood or emotions.”
Post-traumatic stress disorder (PTSD) is a psychiatric disorder that can be triggered by experiencing or viewing a traumatic event, such as a natural disaster, serious accident, hostage-taking, or attack. It manifests itself through vivid flashbacks and avoidance behaviors, such as staying away from places or people that remind them of the traumatic event. Currently, the disorder is treated with psychotherapy or medications, such as antidepressants, but many patients do not respond effectively to them.
Two powerful shocks in different contexts triggered PTSD in mice
In a recent study, published in the journal Molecular Psychiatryresearchers from the universities of Toronto (Canada) and Kyushu (Japan) wanted to know if neurogenesis, that is to say the process of formation of new neurons, in the hippocampus, had an impact on the capacity to forget traumatic memories. As a reminder, the hippocampus, a brain region important for the formation of memories linked to specific places and contexts, produces new neurons daily in an area called the “dentate gyrus”.
To find out, they conducted an experiment on mice. The team gave the rodents two powerful shocks in different settings. First, the animals were shocked after leaving a brightly lit white box and entering a dark, ethanol-scented compartment. After the second shock in a different environment, the mice showed behaviors similar to those of post-traumatic stress disorder. More than a month later, they were still fearful and reluctant to enter the original dark compartment, indicating that they could not forget the traumatic memory. This fear extended to other dark compartments, indicating a generalized fear. In addition, the mice explored open spaces less and avoided the center, suggesting anxiety.
Physical exercise stimulated neurogenesis and reduced severity of PTSD-related behaviors
Next, the scientists looked at whether these behaviors could be mitigated by exercise, which other research suggests stimulates neurogenesis. Rodents that received two powerful shocks were divided into two groups, and one group was given an activity wheel. Four weeks later, the exercised animals had more newly formed neurons in their hippocampi. Another finding: The behaviors associated with post-traumatic stress disorder were less severe than those in mice that didn’t have access to the wheel.
“It may be that neurogenesis and remodeling of hippocampal circuits disrupt fear memory, but have less effect on mood or emotion. Exercise also has broader physiological effects, which may contribute to the better results observed,” has explained Risako Fujikawalead author of the study. In future work, the authors plan to find a drug that can stimulate neurogenesis or hippocampal remodeling, in the hopes that it could be tested as a potential treatment for post-traumatic stress disorder.
