Rutgers Study Explores How the Brain Associates Smells with Fear Responses

The study, published in Nature Communications and led by John McGann from the Department of Psychology, focuses on how a single sensory stimulus—such as an odor, sound, or image—activates various neurons across the brain. This activation can overlap for similar stimuli, complicating the brain's ability to differentiate between the original threat and related stimuli. To assist in this differentiation, referred to as “sensory discrimination,” the brain establishes so-called “fear boundaries” to limit neuron activation to those stimuli associated with danger.

In their experiments, McGann and his team trained mice to connect a specific odor with a mild threat. They then monitored neural activity as the mice reacted to this conditioned odor and a range of new, similar, and dissimilar smells. Natalia Efimova, a first-year doctoral student in McGann’s lab, contributed to the study. The researchers concentrated on the olfactory bulb, a brain area crucial for smell processing, and controlled local inhibitory circuits using pharmacological micro-infusions.

The findings indicate that sensory discrimination and the establishment of fear boundaries occur in the early parts of sensory processing. By altering inhibitory circuits in the olfactory bulbs of the mice, the researchers could influence how easily these animals generalized their fear response to related odors. Each threatening experience also modified the inhibitory circuits in adjacent neurons, leading to the potential misinterpretation of similar stimuli as dangerous.

McGann noted that these results imply the brain starts defining boundaries between dangerous and safe stimuli earlier in sensory processing than previously believed. He suggested that interventions combining sensory training with drugs that influence neurotransmission may be effective for addressing fear generalization in anxiety and PTSD.

Inhibitory processing in the olfactory bulb does not merely transmit sensory information but actively regulates how fear-related neuronal activation spreads, affecting various stimuli. The sensory processing region plays a vital role in determining whether a new odor is threatening or safe based on its similarity to previously encountered dangers.

McGann concluded that overly generalized fears likely stem not just from changes in higher brain regions known for emotion and memory but also from early alterations in how the brain encodes sensory information.