Project Summary Exposure to traumatic events can result in intrusive fear memories that can be evoked not only by stimuli that were present during the event, but also by stimuli that have gained the ability to activate fear through higher- order process despite never being directly paired with trauma. Such fear memories are adaptive but can also contribute to the development of post-traumatic stress disorder (PTSD), with patients often experiencing flashbacks and/or reoccurring memories related to the traumatic event. While a large body of research has focused on identifying the neural substrates responsible for fear memories retrieved by stimuli that were present and directly associated with trauma, much less is known about encoding and retrieval of higher-order conditioning, which allows stimuli not present at the time of trauma to evoke fear responses. It is therefore important to understand the neural substrates that support the encoding and retrieval of higher-order fear memories. Without this knowledge, determining the precise relationship between intrusive memories and PTSD is unlikely. To address this, the proposed research will use chemogenetic and in vivo electrophysiological recording methods in freely moving rats to investigate the necessity of network signal properties underlying the encoding and retrieval of higher-order conditioning, and their coordination across cortical regions. This contribution is expected to be significant because it will yield a detailed understanding of the neural substrates of adaptive higher-order fear memories, which may inform the link between intrusive maladaptive memories and PTSD. Such findings also have the potential to inform treatments for PTSD, especially trauma-focused therapies, in which patients specifically focus on the memory of the trauma or other trauma reminders.