How Memory Changes

March 20, 2026

Researchers at The Hospital for Sick Children (SickKids) revealed that stress alters how our brain encodes and retrieves aversive memories, and they developed a potential new method for restoring adequate memory specificity in persons suffering from post-traumatic stress disorder (PTSD).

If you stumble during a presentation, you might feel stressed the next time you have to present because your brain associates your next presentation with that one poor and aversive experience. This type of stress is tied to one memory. But stress from traumatic events like violence or generalized anxiety disorder can spread far beyond the original event, known as stress-induced aversive memory generalization, where fireworks or car backfires can trigger seemingly unrelated fearful memories and derail your entire day. In the case of PTSD, it can cause much greater negative consequences.

In a study published in Cell, Drs. Sheena Josselyn and Paul Frankland, Senior Scientists in the Neurosciences & Mental Health program, identify the biological processes behind stress-induced aversive memory generalization and highlight an intervention which could help restore appropriate memory specificity for people with PTSD.

“A little bit of stress is good, it’s what gets you up in the morning when your alarm goes off, but too much stress can be debilitating,” says Josselyn, who holds a Canada Research Chair in Circuit Basis of Memory. “We know that people with PTSD show fearful responses to safe situations or environments, and have found a way to limit this fearful response to specific situations and potentially reduce the harmful effects of PTSD.”

Together with their colleague Dr. Matthew Hill at the University of Calgary Hotchkiss Brain Institute, the research team was able to block endocannabinoid receptors on interneurons, and limit stress-induced aversive memory generalization to the specific, appropriate memory.