Researchers at McGill University and University of Toronto-Scarborough discovered that fear may blur the distinction between safe and dangerous experiences rather than sharpen it. The finding, published in Nature Neuroscience, challenges the long-held assumption that fear helps the brain separate threatening from harmless situations.
In experiments with mice, the team trained animals to associate one environment with danger and another with safety. Rather than developing increasingly separate neural representations of the two locations, the animals' brain activity showed overlapping patterns as fear responses strengthened. The researchers used augmented reality combined with real-time brain imaging to observe this process. Miniature microscopes monitored hundreds of neurons in the hippocampus while the mice experienced virtual transitions between safe and dangerous settings.
"Our findings suggest fear may blur the boundary between danger and safety rather than sharpen it," said Mark Brandon, Associate Professor in McGill's Department of Psychiatry and senior author. "This could reshape how scientists think about anxiety and PTSD."
The overlapping memory representations may serve an evolutionary purpose. By mixing memories of safe and dangerous experiences, the brain can retrieve threat information more rapidly, allowing faster responses to potential danger. This strategy prioritizes speed over accuracy.
"The ventral hippocampus may be part of a system that prioritizes a rapid 'better safe than sorry' response," said Robert Rozeske, lead author and Assistant Professor at University of Toronto's Department of Psychology. "In other words, the brain may sacrifice precision for speed when danger matters."
The findings may explain why people with anxiety and PTSD experience intense fear responses in objectively safe situations. Mark Brandon suggested these reactions may reflect an overactive version of a normal survival mechanism rather than a broken system. The researchers note that additional research is needed to determine whether these mechanisms operate similarly in humans, as the experiments used mice.