What is it that a neurobiological model of PTSD must explain?

PTSD is a complex disorder that involves far more than a fear response, and cannot be explained by a simple conditioning model. Both individual vulnerability and specific reactions during and after the trauma are involved in maintaining the disorder. A consideration of risk factors implicates the experience of being "overwhelmed" at the time of the trauma, accompanied by possible downregulation of the prefrontal cortex. Also important are reactions to symptoms post-trauma and specific strategies adopted to manage symptoms, such that there is a continuing inability to process trauma memories. An analysis of the characteristic forms of autobiographical memory in PTSD implicates two memory systems, one predominantly image-based and one predominantly verbal. These systems are likely to be differentially impacted by hormonal responses to extreme stress, leading to an imbalance in the representation of trauma in the two systems. Exposure to trauma reminders leads to retrieval competition between the two sets of memories, with retrieval of verbal memories able to inhibit inappropriate amygdala responses. Evidence to support this analysis is described, drawing on experimental studies of memory for trauma and a meta-analysis of memory for emotionally neutral information in PTSD. The implications for neurobiological studies of PTSD are discussed.