By Abbas Nazil
Scientists have discovered a critical brain mechanism that determines whether animals freeze or flee when faced with a threat, offering new insight into instinctive behavior and potential treatments for anxiety disorders.
At the core of this discovery is a tiny structure deep in the brain known as the dorsal periaqueductal gray (dPAG), a region long known to be responsible for triggering defensive reactions in mammals.
Researchers from Harvard University and the Vlaams Instituut voor Biotechnologie (VIB) in Belgium studied two closely related deer mouse species with drastically different responses to predators.
The study, published in Nature, shows that both species perceive threats equally well, as their visual and auditory processing pathways react identically to stimuli.
However, their behaviors differ because of how their dPAG neurons respond.
In forest mice, minimal visual cues trigger intense firing of neurons in the dPAG, corresponding with rapid escape.
In contrast, prairie mice require much stronger stimuli to activate their dPAG and begin to flee.
Using advanced tools like Neuropixels probes and optogenetics, the team showed that the threshold for activating this brain region varies between species based on habitat needs.
By artificially stimulating the dPAG in forest mice, researchers caused them to flee even in safe environments.
Prairie mice, however, showed little or no reaction to the same stimulation.
Chemogenetic suppression of the dPAG in forest mice made them behave more like their prairie counterparts, suggesting that subtle neural adjustments in this midbrain region drive behavioral differences.
These results suggest that evolution has fine-tuned the sensitivity of the escape response by adjusting a central brain circuit rather than altering sensory perception or building entirely new neural pathways.
This finding challenges the assumption that core survival behaviors are rigid and unchangeable across species.
It also demonstrates that evolutionary pressure can act efficiently on internal thresholds to adapt to environmental conditions.
The implications go beyond animal behavior.
Because the dPAG and related brainstem structures are also involved in human fear and panic, this research may open new avenues for treating anxiety and stress-related disorders.
Rather than blocking fear responses entirely, therapies could aim to recalibrate the brain’s sensitivity to threats.
The study highlights how evolution conserves key brain structures while enabling flexible behavioral adaptations through subtle changes in neural responsiveness.
