Rutgers Study Examines Brain Mechanisms in Fear Response and Sensory Discrimination

This study, published in *Nature Communications*, was led by John McGann, a professor in the Department of Psychology at Rutgers University–New Brunswick. The researchers focused on how a single sensory stimulus, such as an odor, sound, or image, activates numerous overlapping neurons in the brain. When recalling a fear-inducing experience, the brain must decide which stimuli to avoid based on the degree of neural overlap, establishing what they termed “fear boundaries.”

To investigate the neural basis of smell-associated fear responses, McGann and his team trained mice to link a specific odor with a mild threat. They then observed the neural activity as the mice responded to both the conditioned odor and various similar and dissimilar smells. Natalia Efimova, a first-year doctoral student in McGann's lab, was a contributor to the study. The researchers focused on the olfactory bulb, a brain region crucial for processing smells, and utilized pharmacological micro-infusions to manipulate local circuits and assess how these changes impacted sensory processing and fear discrimination.

Efimova noted that their findings revealed sensory discrimination and the formation of fear boundaries occur in the early sensory processing areas of the brain. By altering inhibitory circuits in the olfactory bulb, the team was able to influence how easily the mice generalized their fear to related odors. This adaptability indicates that when an animal experiences danger tied to a specific odor, the circuits in nearby neurons also become modified, increasing the likelihood that similar smells will trigger a fear response.

McGann emphasized that these results suggest the brain identifies boundaries between dangerous and safe stimuli earlier in sensory processing than previously thought. He proposed that incorporating sensory training or exposure therapy along with pharmacological interventions may be beneficial in treating fear generalization in anxiety and PTSD.

The study also highlights the active role of inhibitory processing in the olfactory bulb, which not only transmits sensory information but also modulates how neuronal activation spreads after a frightening experience. This processing aids the brain in determining whether a new smell resembles a previously threatening odor enough to invoke fear or is distinct enough to be deemed safe.

McGann concluded that overly generalized fears may stem from neuroplastic changes not only in higher brain regions responsible for emotion and memory but also in early sensory processing stages.