Scientists have identified a part of the brain involved in inhibiting fear, a discovery that holds potential for helping patients with psychiatric diseases such as post-traumatic stress disorder (PTSD).
The findings of a new study, which appears in Nature Communications, shows that a small brain region in the thalamus called the nucleus reuniens plays a role in inhibiting fear in rats.
Prior to the discovery, the region was thought to act primarily as a pathway by which sensory information travels from the periphery of the brain to the cortex, the part responsible for performing complex thought.
“It’s interesting because we know that the prefrontal cortex plays an emotion regulation role, and so there has been a lot of interest in how it accomplishes that,” says Stephen Maren, distinguished professor of psychological and brain sciences at Texas A&M University.
“So this basic research, identifying this particular projection from the prefrontal cortex to the nucleus reuniens in the thalamus, points us to parts of the brain that are important for the inhibitory function of fear, which could be an avenue to new drugs, therapies, and interventions for psychiatric disorders,” Maren says.
Currently, most drugs that physicians use to treat psychiatric disorders are indiscriminate and target all neurons in the brain. However, behavioral therapies, such as extinction therapy for PTSD, during which patients undergo prolonged, repetitive exposure to their traumas in safe settings, are effective in diminishing fear, but patients often relapse.
For the study, Maren and colleagues exposed rats to tones paired initially with mild foot shocks to create the fear response. They then used an extinction procedure, exposing the rats to the tones repetitively for prolonged periods, to suppress the fear.
Using a pharmacological approach, Maren and his team inactivated the nucleus reuniens and found that rats were unable to suppress fear. They next used a targeted pharmacogenetic strategy to silence neurons selectively in the prefrontal cortex projecting to the reuniens. To do this, Maren and his team used engineered viruses carrying designer receptors exclusively activated by designer drugs (DREADDs). They found that inhibiting these inputs also prevented rats from suppressing fear.
By identifying the involvement of this specific circuit of the brain in fear inhibition, researchers can now pursue more targeted treatments for psychiatric disorders that work better and last longer.
The National Institutes of Mental Health, the McKnight Endowment Fund for Neuroscience and the Brain and Behavior Research Foundation funded this study.
Source: Texas A&M University