Individuals with fear disorders such as post-traumatic stress disorder (PTSD) experience excessively strong and intrusive fear memories about stimuli that were encountered during a prior trauma, including individual sounds or visual stimuli (?cue-specific? fear memory) or the combination of stimuli that together define the place in which the event occurred (?contextual? fear memory). The memories may have been formed recently or long ago (?remote? memories), in which case they may plague a person for a substantial portion of his/her life. The development of effective therapies depends on a thorough understanding the neural mechanisms that underlie these different types of fear memories, as well as fear extinction, which is the basis for exposure- based therapy commonly used to reduce fear in humans. To date, a substantial body of research has identified discrete neural systems that support recent versus remote contextual memory, and other studies have identified the substrates of recently-acquired cue-specific memory and extinction, but very little work has focused on the brain mechanisms involved in remote cue- specific memory and extinction. This is important to resolve particularly with respect to PTSD since individuals often do not seek therapy until long after the traumatic event, especially in cases of combat trauma or sexual assault. To address this, the proposed research advances a new theoretical model of the neural circuits that underlie remote cue-specific fear memory and extinction. This model is based on new data from our laboratory and combines state-of-the art chemogenetic and optogentic-anatomical approaches to test the hypotheses that a) communication between the retrosplenial cortex and secondary sensory cortices is necessary for remote cue-specific fear memory, and b) the postrhinal cortex mediates the context-dependency of extinction of remote cue-specific fear.
Exposure to highly emotional or traumatic events can lead to fear-related memories that are maladaptive. A standard approach to treating persons who experience inappropriate or excessive fear is exposure (extinction) therapy, which seeks to reduce conditioned fear via repeated presentation of the fear-eliciting stimulus in the absence of an aversive outcome. Here, we will carry out the first studies aimed at identifying the neural systems that mediate memory and extinction of specific fear memories that were formed long ago. This is particularly important because many persons with disorders such as PTSD do not seek treatment for a prolonged period of time after the traumatic event that produced the fear memory.