Research from the Douglas Research Centre at McGill University and the University of Toronto-Scarborough has revealed a surprising aspect of memory storage in the brain that may provide insight into the symptoms associated with anxiety and post-traumatic stress disorder (PTSD). Published in Nature Neuroscience, the study challenges the long-held belief that fear sharpens the distinction between danger and safety.
The researchers conducted preclinical experiments involving mice, where the animals were conditioned to associate one environment with danger and another with safety. Instead of forming distinct memories, the brain maps for these environments began to overlap.
“Our findings suggest fear may blur the boundary between danger and safety rather than sharpen it,” said Mark Brandon, senior author of the study and Associate Professor in McGill’s Department of Psychiatry. He noted that this new understanding could significantly alter the scientific perspective on anxiety and PTSD.
Augmented Reality Innovations
To examine the brain’s response, researchers created an augmented reality arena that allowed them to “teleport” mice between the dangerous and safe environments, accompanied by varying visual and auditory cues. Using miniature microscopes, they recorded the activity of hundreds of hippocampal neurons in real-time as the mice transitioned between these competing memory contexts.
“That gave us something conventional fear conditioning experiments cannot easily provide: a moment-by-moment view of the brain switching between competing maps of dangerous and safe memories,” explained Robert Rozeske, the study’s lead author and Assistant Professor in the University of Toronto’s Department of Psychology.
Survival Mechanism Insight
The overlapping memory phenomenon may represent a survival strategy rather than a malfunction in the brain’s memory systems, the researchers suggested. In their findings, overlapping memories facilitated quicker recall of past threats, enabling faster responses to potential dangers.
“The ventral hippocampus may be part of a system that prioritizes a rapid ‘better safe than sorry’ response,” Rozeske noted. He emphasized that this mechanism may prioritize speed over precision in life-threatening situations.
For individuals with anxiety and trauma-related disorders, seemingly safe situations can trigger intense fear as certain memories resurface. Brandon added, “Our study suggests that’s not necessarily a broken pattern-separation system, but possibly an overactive version of a normal survival mechanism gone into overdrive.” This reframing of the issue could inform future therapeutic approaches aimed at managing rapid transitions to a heightened state of alertness.
Reference: Rozeske RR, Runtz L, Lee JQ, Keinath AT, Sossin A, Brandon MP. Overlapping representations in the ventral hippocampus support rapid fear memory retrieval. Nat Neurosci. 2026. doi: 10.1038/s41593-026-02435-5
