The brain’s fear response, long understood as a way to distinguish danger from safety, may instead blur those boundaries, scientists report. In a study led by researchers at the Douglas Research Centre at McGill University and the University of Toronto Scarborough, mice were trained to link one environment with danger and another with safety. The research, published in Nature Neuroscience, suggests fear can make the brain’s representations of safe and dangerous experiences overlap.
“Our findings suggest fear may blur the boundary between danger and safety rather than sharpen it,” said senior author Mark Brandon, Associate Professor in McGill’s Department of Psychiatry and Researcher at the Douglas. “This could reshape how scientists think about anxiety and PTSD.”
To observe how these changes unfold, the team built an arena that used augmented reality to shuttle mice between virtual risk and safety, while miniature microscopes tracked hundreds of neurons in the hippocampus. This approach allowed a moment-by-moment view of the brain as animals moved between experiences associated with safety and threat.
“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,” said Robert Rozeske, Assistant Professor in the University of Toronto’s Department of Psychology and lead author on the publication.
The researchers propose that overlapping memory representations may help retrieve information about potential threats more rapidly, enabling quick recognition and response. The ventral hippocampus, they suggest, may be part of a system that prioritises a rapid “better safe than sorry” response. “In other words, the brain may sacrifice precision for speed when danger matters,” Rozeske added.
The findings could shed light on why people with anxiety and trauma-related disorders sometimes experience powerful fear responses in settings that pose no immediate threat. The researchers say such reactions may arise, at least in part, when a normally useful survival mechanism becomes excessively sensitive, rather than simply reflecting a failure to distinguish memories.
“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,” Brandon commented. “That reframing could guide therapeutic approaches to address an overly fast transition to ‘danger mode’.”
Because the experiments were conducted in mice, further research is required to determine whether the same mechanisms operate in humans. Nonetheless, the work offers a new lens on how fear shapes memory and why a brain system designed to protect against danger might sometimes generate fear when no immediate threat exists.
The study, “Overlapping representations in the ventral hippocampus support rapid fear memory retrieval,” was published with funding from the Canadian Institutes of Health Research and the Natural Sciences and Engineering Research Council of Canada, and by researchers Robert Rozeske and Mark Brandon.
