Why Do Some Stressful Events Stay Vivid While Others Turn into Generalized Fears?

Recent research has uncovered a striking phenomenon: stress not only enhances the intensity of memories but can also distort them, causing harmless situations to be perceived as threatening. The research team, led by Prof. Sheena Josselyn at the University of Toronto (Canada), has demonstrated that, under stress, the brain engages a larger-than-usual population of neurons to encode negative memories. This neuronal overload, attributed to a dysregulation of the endocannabinoid system, creates a pervasive alarm signal that obscures the distinction between safety and danger.

This mechanism is central to the development of stress-related disorders, such as post-traumatic stress disorder (PTSD). Gaining deeper insights into how stress influences memory formation offers promising opportunities for the development of novel pharmacological interventions.

Lesuis, S. L., Park, S., Hoorn, A., Rashid, A. J., Mocle, A. J., Salter, E. W., Vislavski, S., Gray, M. T., Torelli, A. M., DeCristofaro, A., Driever, W. P. F., van der Stelt, M., Zweifel, L. S., Collingridge, G. L., Lefebvre, J. L., Walters, B. J., Frankland, P. W., Hill, M. N., & Josselyn, S. A. (2025). Stress disrupts engram ensembles in lateral amygdala to generalize threat memory in mice. Cell, 188(1), 121–140.e20. https://doi.org/10.1016/j.cell.2024.10.034