Texas A&M University researchers have identified a new brain region that is said to inhibit fear – a finding that scientists say could hold the potential for clinical interventions in patients with psychiatric diseases such as post-traumatic stress disorder (PTSD).
Scientists at the university discovered that a small brain region in the thalamus called the nucleus reuniens plays a role in inhibiting fear in rats. Prior to this findings, it was believed that this particular region of the brain acted 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.
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 researchers 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 researchers 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 article was published in Nature Communications on Oct. 30.