Brain pathways of traumatic memory: Evidence from an animal model of PTSD

Memory is distinctly advantageous for survival. The ability of an organism to form and retain a record, especially of threatening events, to accumulate and maintain this information in a manner that allows ready access and ongoing updating, i.e., to form memories, confers the ability to anticipate danger and prepare for or avoid it. Memory is a core feature of posttraumatic stress disorder (PTSD), which in one way or another is involved in the majority of trauma-related phenomena. Trauma memories themselves behave differently from other memories and characteristically persist, almost unchanged, while maintaining their exceedingly vivid and real quality. The memories tend to intrude in the form of flashbacks and nightmares and are highly responsive to reminders of the traumatic events. Paradoxically, they are often fragmented, and the hypermnesia is often accompanied by patches of amnesia. The recent growth of knowledge relating to the neurobiology of emotional memory has led to proposals for potential pharmacological interventions, specifically designed to decrease or prevent PTSD, by targeting memory mechanisms. On the biological level, there are two phases during which memory traces are sufficiently unstable as to render them potentially amenable to the effects of experimental (pharmacological) interventions. The first is during initial consolidation from the temporary short-term memory format to the stable and enduring long-term memory format and the second while they are temporarily reactivated (normally, for ongoing use and updating), prior to being reconsolidated. This chapter describes the behavioral findings of a series of animal studies, which focused on the effects of various interventions on aspects related to memory, using an animal model for PTSD. The data analysis pivots on the post-factum classification of subjects according to three levels of severity of disruption in behavioral responses.