MIT Neuroscientists Identify Brain Signal That Actively Suppresses Fear

Neuroscientists at the Massachusetts Institute of Technology (MIT) have identified a specific dopamine signal in the brain that actively triggers the extinction of fear once a threat has passed—a discovery that could pave the way for new treatments for post-traumatic stress disorder (PTSD). The findings were published in the Proceedings of the National Academy of Sciences (PNAS).

The study focused on two types of neurons in the brain's basolateral amygdala (BLA): one promotes fear, while the other suppresses it. Previous research had linked dopamine released from the ventral tegmental area (VTA) to fear extinction, but the underlying mechanism remained unclear.

To explore this, researchers injected fluorescent tracers into the brains of mice and found that the VTA sends dopamine signals to both fear-activating and fear-suppressing neurons in the BLA. Using genetically modified mice whose dopamine activity could be tracked via fluorescence, the team recorded brain activity with optical fibers. When mice were re-exposed to an environment where they had previously received a shock—but without any threat present—the dopamine signal in fear-suppressing neurons increased significantly, leading to a gradual calming response.

In further experiments, scientists used optogenetics to enhance dopamine signaling from the VTA to the fear-suppressing neurons in the BLA. This intervention accelerated fear extinction in the mice, suggesting that targeted modulation of dopamine pathways could facilitate the erasure of fear memories.

While humans share similar brain structures involved in fear regulation, additional research is needed to determine the applicability of these findings to human PTSD treatment. Nonetheless, the study highlights BLA neurons as a promising therapeutic target for fear-related disorders.