The reason for the connection between stress and memory loss is due to an immune system reaction. As the body goes through a physiological change to an unpleasant (stressful) event, this triggers an immune reaction. One side of the immune response can be inflammation.
The findings are based on animal models. In the study, a test group of mice were exposed to an aggressive, larger, alpha mouse on multiple occasions. The test mice were placed under chronic stress, such as losing out on food or being attacked by the larger mouse. After a period of time it was shown that key things that the mice had previously remembered had been forgotten, such as remembering where the escape hole was in a maze. The mice also displayed behavior similar to depression, for several weeks after their last exposure to the more aggressive mouse.
Comparative studies on control mice, not subjected to the same levels of stress, showed that stress was the factor and not anything else to do with age, food or environment.
Surgical studies carried out on the mice after the study showed inflammation associated with the presence of immune cells (a type known as macrophages) in the brain. There was also a noticeable reduction in brain neurons with the mice subjected to the high-level of stress.
With a second round of studies, test mice were administered an immune blocker. In this study they did not forget the escape hole, and the surgical investigation showed no significant level of inflammation.
In a research note, the lead scientist, Professor Johnathan Godbout stated: “The stressed mice didn’t recall it. The mice that weren’t stressed really remembered it.”
Due to similarities with the neural connections of the brains of mice compared with people, the researchers think similar effects could occur with people who are subjected to continual patterns of stress.
The research was conducted at Ohio State University. The findings are published in The Journal of Neuroscience, in a paper titled “Neuroinflammatory Dynamics Underlie Memory Impairments after Repeated Social Defeat.”