Posterior parietal cortex mediates fear renewal in a novel context.

The return of fear following extinction therapy is an important issue associated with the treatment of many fear-related disorders. Fear renewal is a suitable model, with which context-dependent modulation of the fear response can be examined. In this model, any context outside of an extinction context (e.g., novel or familiar contexts) could evoke relapse of the fear response. However, brain regions associated with context-dependent modulation are not fully understood. The posterior parietal cortex (PPC) is considered a center for integrating multisensory information and making decisions. To study its role in the contextual modulation of fear relapse, we reversibly inactivated the PPC in mice before they were exposed to various contexts after extinction training. When muscimol was infused into the PPC, fear renewal was impaired in a novel context, but not in a familiar context. Fear relapses were blocked during optogenetic inhibition of the PPC, only when animals were placed in a novel context. We propose that the neural activity of the PPC is necessary for the relapse of a precise response to an extinguished conditioned stimulus in a novel context.