Unraveling trauma memory: Differential functional connectivity profiles of anterior and posterior hippocampus in post-traumatic stress disorder and its dissociative subtype

Abstract

Post-traumatic stress disorder (PTSD) has long been viewed by many as a disorder of memory. Consequently, the hippocampal brain networks have been an important focus of research on the neural circuitry of PTSD given its core involvement in episodic memory and mechanisms underlying traumatic memory. The primate hippocampus is functionally divided along its long axis into the anterior (aHipp) and posterior parts (pHipp), with the anterior portion playing a greater role in emotion-related memories, while the posterior region is more involved in cognitive and spatial processing. This suggests that the aHipp may be more actively involved in PTSD. Critically, however, little research has investigated the differential involvement of these hippocampal subregions in PTSD, and most research in this area has been conducted during rest rather than during the active recall of traumatic or extremely emotional memories. It is an open question whether anterior and posterior hippocampal regions might play differential roles during trauma-related memory recall. Here, we addressed this question by investigating the activity and the whole-brain functional connectivity of the aHipp and pHipp during the recall of traumatic/moral injury (MI) related trauma memories versus neutral memories in three groups: those with PTSD without dissociative symptoms, referred to as PTSD (DS-; n = 49), those with the dissociative subtype, referred to as PTSD (DS+; n = 19), and trauma-exposed healthy controls (n = 36). Both anterior and posterior hippocampal subregions displayed abnormal functional connectivity with various brain regions in PTSD (DS+) during trauma memory recall, with the pHipp showing more extensive abnormalities compared to the anterior part. For example, the pHipp showed abnormal functional connectivity with areas such as the anterior cerebellum, the parahippocampal and fusiform gyri, sensorimotor cortex, and early visual areas of the occipital lobe in PTSD (DS+) compared to PTSD (DS-) and controls during the recall of traumatic/MI memories. Collectively, these results suggest differential involvement of the anterior and posterior hippocampus in the recall of traumatic memories in traumatic/MI-related PTSD and its dissociative subtype, which may relate to the decontextualized and fragmented nature of traumatic memories.