A review of hippocampal activation in post‐traumatic stress disorder

Abstract

Post‐traumatic stress disorder (PTSD) is often characterized by deficits in memory encoding and retrieval and aberrant fear and extinction learning. The hippocampus plays a critical role in memory and contextual processing and has been implicated in intrinsic functional connectivity networks involved in self‐referential thought and memory‐related processes. This review focuses on hippocampal activation findings during memory and fear and extinction learning tasks, as well as resting state hippocampal connectivity in individuals with PTSD. A preponderance of functional neuroimaging studies to date, using memory, fear learning, and extinction tasks, report decreased or “controls comparable” hippocampal activation in individuals with PTSD, which is usually associated with poorer performance on the task imaged. Existing evidence thus raises the possibility that greater hippocampal recruitment in PTSD participants may be required for similar performance levels. Studies of resting state functional connectivity in PTSD predominantly report reduced within‐network connectivity in the default mode network (DMN), as well as greater coupling between the DMN and salience network (SN) via the hippocampus. Together, these findings suggest that deficient hippocampal activation in PTSD may be associated with poorer performance during memory, extinction recall, and fear renewal tasks. Furthermore, studies of resting state connectivity implicate the hippocampus in decreased within‐network DMN connectivity and greater coupling with SN regions characteristic of PTSD.

Psychophysiological approaches to understanding the impact of trauma exposure

“…The selection of articles further reflects the range of measures leveraged in current research on the psychophysiology of trauma exposure. Selected articles demonstrate the utility of fear‐potentiated startle ( Jovanovic et al, 2019; Lis et al, 2019), heart rate ( Grupe et al, 2019; Iffland et al, 2019), and ERPs to decode the translation of trauma exposure into PTSD symptoms ( Macatee et al, 2019; Sill et al, ), together with the power of hemodynamic imaging by means of BOLD responses during emotional scene processing ( Sambuco et al, 2019) or resting‐state connectivity ( Harricharan et al, 2019; Joshi, Duval, Kubat, & Liberzon, 2019).…”

“…Current evidence further elucidates the role of the hippocampus, insula, and fronto‐cortical networks in shaping learning and memory after traumatic experiences: Joshi et al (2019) provide a comprehensive review of hippocampal activation and resting‐state connectivity during memory, fear, and extinction learning tasks. They conclude that trauma‐induced hippocampal dysfunction is characterized by decreased within‐network connectivity but accentuated coupling with the salience network.…”

Neural Bases of Cognitive Impairments in Post-Traumatic Stress Disorders: A Mini-Review of Functional Magnetic Resonance Imaging Findings

“…Finally, it has also been reported that PTSD patients had altered activity in the hippocampus while processing a memory task (13). This finding is not surprising, especially because a robust body of literature in the last decades has consistently reported the key role played by the hippocampus in declarative memory (encoding and retrieving information), semantic and episodic memory, as well as in emotional memory [for recent reviews, see (41,42)]. Furthermore, this result is also supported by behavioral data, suggesting that subjects affected by PTSD have poor performance in memory tasks, including both neutral and emotional stimuli, as well as severe difficulties in retrieving neutral words and autobiographical episodes (42).…”

Five Applications of Narrative Exposure Therapy for Children and Adolescents Presenting With Post-Traumatic Stress Disorders

“…Thus, when triggered, "hot" memories for traumatic events (including the emotional, cognitive, sensory, and physiological experiences of the event) are more likely to be experienced in the absence of the temporal and spatial contextual information (cold memory) associated with the event. Although the neurological processes involved are highly complex (20,21), these disturbances can, for example, lead to the subjective experience of a "flashback"-when the event is re-experienced in the here and now. In PTSD, this can lead to a fear of encountering any possible memories and triggers of the original event.…”