Neural circuits and mechanisms involved in fear generalization: Implications for the pathophysiology and treatment of posttraumatic stress disorder

Compelling evidence suggests that fear generalization (i.e. the transfer of fear from a particular stimulus to another one sharing similarities with the original stimulus) may contribute to the development of posttraumatic stress disorder (PTSD), for which current treatments are ineffective. Deficits in hippocampus-mediated pattern separation, the process by which memories are stored as unique representations that are resistant to confusion, have been solely proposed as a putative underlying marker of generalization. We delineate instead an enlarged scenario, wherein conditioned and generalized fear memories share a common neurocircuitry, with the hippocampus being the nub of contextual fear, and the prefrontal cortex of both cued and contextual fear. The potential contribution of the amygdala and insula will be highlighted as well. Finally, we will consider vulnerability factors that may contribute to the development of PTSD, and suggest avenues for novel therapeutics. A better understanding of the mechanisms behind fear generalization is fundamental to provide further insight into treatment of debilitating conditions such as PTSD.