Differential Roles of the Anterior and Posterior Hippocampus During Trauma Memory Recall in Post-Traumatic Stress Disorder and Its Dissociative Subtype

Abstract

Post-traumatic stress disorder (PTSD) is a psychiatric condition that may occur after exposure to a traumatic event such as sexual assault. One of its most noticeable adverse effects is abnormality in recalling traumatic memories, leading to severe distress and the sensation that the trauma is unfolding in the present moment. The dissociative subtype of PTSD (PTSD+DS) is a distinct form of PTSD with rather different symptoms, including emotional numbing and dissociative symptoms of depersonalization and derealization. Individuals with PTSD+DS tend to recall trauma memories from an out-of-body or third- person perspective, presumably as a maladaptive mechanism to distance themselves from the trauma. Many brain areas involved in episodic memory exhibit structural and functional abnormalities in PTSD, including the hippocampus, a core component of the episodic memory system. However, findings regarding the hippocampal role in the neurocircuitry of PTSD are rather inconsistent. These inconsistencies may stem from the often overlooked different functions of the anterior (aHipp) and posterior hippocampus (pHipp). The aHipp is primarily involved in processing the emotional aspects of episodic memories, while the pHipp is more involved in spatial and contextual processing. We therefore hypothesized that the aHipp would be more dominant during trauma memory recall in classic PTSD compared to the pHipp. In PTSD+DS, we expected the dominance of the aHipp to di- minish. Our findings mainly supported our predictions. Graph-theoretic analyses revealed the aHipp to be a dominant hub in the brain in classic PTSD during both resting state and trauma memory recall. In PTSD+DS, however, the aHipp did not emerge as a hub, and instead, the pHipp assumed a more pronounced role. Our findings advance the current understanding of the hippocampal roles in PTSD and PTSD+DS and may guide future therapeutic efforts.