Post-traumatic stress disorder is a disabling condition that may affect individuals who have been exposed to severe emotional or physically life-threatening traumatic events. The majority of neuroimaging studies of post-traumatic stress disorder have focused on potential abnormalities in the hippocampus, a brain area that plays a critical role in memory processing and biological response to stress. Most of the imaging studies have found smaller volume of the hippocampus as measured with magnetic resonance imaging in patients with post-traumatic stress disorder while others failed to reveal hippocampal volume loss. We reviewed magnetic resonance imaging researches which focused on the hippocampal structural alteration of post-traumatic stress disorder in different populations (adults and children), with different research design (cross-sectional and longitudinal), and using different volume measure protocols (hippocampal total volume and subfield volume).
Key words: Hippocampus; Magnetic resonance imaging; Stress disorders, post-traumatic
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Post-traumatic stress disorder (PTSD) is a psychiatric condition in which an individual presents with intrusion, lability of mood, emotional numbness and avoidance after exposure to severe traumatic events. Neuropsychological studies have shown that PTSD patients have impaired attention, working memory, and new learning1; electroencephalography reveals that affected persons have heightened processing of trauma-related information, but weaker processing of neutral information.2 These findings suggest possible structural and functional abnormalities in memory-related brain areas. The hippocampal formation, which plays an important role in memory processes, probably exerts significant effects in the pathogenesis of PTSD.
The hippocampus, an important component of the brain limbic system, is the area that controls learning and memory. While playing a significant role in spatial learning and memory, it is also implicated in anxiety behaviours.3,4 Moreover, functional and structural abnormalities of the hippocampus are believed to be associated with a number of psychiatric disorders. The hippocampus is also one of the brain structures that regulates stress responses. Studies with animals demonstrated that chronic stress may lead to changes in hippocampal structure in rats, including suppression of neurogenesis, neural dendritic atrophy and neuron loss. Changes in hippocampal structure and function are therefore considered to be causally inter-related to the development of many psychiatric diseases.5 Researchers studying the brain structure of patients with PTSD have focused mainly on the hippocampal region. This paper aimed to present an organised and selected review / analysis of relevant published Chinese and English literature on this topic.
Alterations in Hippocampal Formation of Adult Patients with Post-traumatic Stress Disorder
Since the first report by Bremner et al6 in 1995 describing magnetic resonance imaging (MRI) which showed a reduction in right hippocampus volume in PTSD patients compared with the controls, a variety of different reports have been published on this subject. Most of these found that the hippocampal volume of PTSD patients was relatively smaller than that in healthy controls or persons exposed to traumatic events but not suffering from PTSD.
In the study by Bremner et al,6 the hippocampal volume of the right side in veterans with PTSD was about 8% smaller than that in healthy controls, and this reduction in size correlated with defects in declarative memory function. However, the research group also conducted a study on childhood sexual abuse-related PTSD patients, and found that the left hippocampal volume was 12% smaller than that in healthy controls. Despite controlling for different confounders, this difference was still significant,7 whereas there was no significant difference between right hippocampal volumes. …