Hippocampal function in posttraumatic stress disorder

Abstract

Recent studies have reported memory deficits and reduced hippocampal volumes in posttraumatic stress disorder (PTSD). The goal of the current research was to use functional neuroimaging and a validated explicit memory paradigm to examine hippocampal function in PTSD. We used positron emission tomography (PET) and a word-stem completion task to study regional cerebral blood flow (rCBF) in the hippocampus in 16 firefighters: 8 with PTSD (PTSD group) and 8 without PTSD (Control group). During PET scanning, participants viewed three-letter word stems on a computer screen and completed each stem with a word they had previously encoded either deeply (High Recall condition) or shallowly (Low Recall condition). Relative to the Control group, the PTSD group exhibited significantly smaller rCBF increases in the left hippocampus in the High vs Low Recall comparison. However, this finding reflected relatively elevated rCBF in the Low Recall condition in the PTSD group. Collapsing across High and Low Recall conditions, (1) the PTSD group had higher rCBF in bilateral hippocampus and left amygdala than the Control group, and (2) within the PTSD group, symptom severity was positively associated with rCBF in hippocampus and parahippocampal gyrus. The groups did not significantly differ with regard to accuracy scores on the word-stem completion task. The PTSD group had significantly smaller right (and a trend for smaller left) hippocampal volumes than the Control group. The results suggest an abnormal rCBF response in the hippocampus during explicit recollection of nonemotional material in firefighters with PTSD, and that this abnormal response appears to be driven by relatively elevated hippocampal rCBF in the comparison condition.

The role of biomarkers and MEG-based imaging markers in the diagnosis of post-traumatic stress disorder and blast-induced mild traumatic brain injury

“…Functional neuroimaging findings using positron emission topography (PET) and functional magnetic resonance imaging (fMRI) suggest that individuals with PTSD exhibit hyperresponsive amygdala activity to trauma or fear-related stimuli (for review, see Shin and Liberzon, 2010), during emotionally neutral tasks (Bryant et al, 2005;Shin et al, 2004b), and even at rest (Chung et al, 2006;Semple et al, 2000). A hyperresponsive amygdala contributes to the exaggerated fear response characteristic of PTSD (Anderson et al, 2003).…”

Hippocampal volume and declarative memory function in combat-related PTSD

“…Among those 26 studies, 16 reported a smaller hippocampus in PTSD in at least one hemisphere. Of those 16, 10 tested memory, but in one case, this was a test of implicit memory (Shin et al, 2004 ). Of the 9 studies testing declarative memory, 2 did not report whether group differences were found, and only 4 reported signifi cantly worse memory in PTSD.…”

The Transformation of Post-Traumatic Stress Disorder: From Neurosis to Neurobiology

“…Impairment of hippocampal function is also suggested from functional magnetic resonance imaging (fMRI) studies, in which the activity of brain regions is extrapolated from blood flow changes over time. For example, when engaged in verbal learning tasks PTSD patients demonstrate lower levels of hippocampal activation than matched non-PTSD control subjects Shin et al, 2004). Sustained treatment of PTSD for several months with the antidepressant paroxetine produced increases in hippocampal volume and cognitive function .…”