Electrical stimulation of certain brain regions has been used to treat obsessive–compulsive disorder (OCD), but how it works is unknown. Researchers suggest that the stimulation could work by acting on brain circuits involved in dampening fear responses.

Gregory Quirk and his team at the University of Puerto Rico in San Juan implanted electrodes in the brains of rats. The authors conditioned the animals to expect a footshock whenever they heard a tone and then, the next day, exposed the rats to the tone without the shock to extinguish the conditioned fear. When, on the second day, the researchers stimulated a specific area of a brain region similar to that targeted during OCD treatment, the rats later showed less fear on hearing the tone than did control rats. The stimulation also boosted the expression of a marker of plasticity — the ability to reorganize neural pathways — in regions involved in extinguishing fear. This suggests that the brain stimulation enhances fear extinction.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1200782109 (2012)