Recalling positive memories seems to alleviate depression-like behaviours in mice, reports a paper in this week's Nature. The study shows that it is activation of the memory trace associated with a positive event, rather than the positive event itself, that triggers the antidepressant effect. Although the findings may have therapeutic implications, it is currently unclear how they may translate into humans.
Susumu Tonegawa and colleagues identified the specific neural engram (in which memory traces are stored) created when male mice were exposed to female mice, a positive experience, and tagged these neuronal cells so that they could be reactivated with pulses of light. Mice were then subjected to stressful conditions that induced depression-like behaviour. Artificial reactivation of the positive memory traces instantaneously suppressed depression-like behaviour. The authors also showed that repeated reactivation of the positive memory seems to increase resilience to stress-induced depression-like behaviour even after the reactivation had finished, whereas exposure to a positive experience did not.
The positive memory traces reactivated in this study are located in a region of the brain called the hippocampus, which is thought to have a role in regulating stress responses, although the precise mechanisms involved in this process are unknown.