Stress-induced anatomical changes in white and gray matter: a review of literature

Post traumatic stress disorder (PTSD) is a psychiatric abnormality caused by a drastic traumatic event or extreme stress, that exceeds the capability to adapt. There are many papers reporting anatomical brain changes induced by trauma and extreme stress, not only in white matter but in gray matter as well. Extreme stress and trauma are connected with elevation of cortisol level, which may cause damage to the hippocampus and may interfere with the anatomy of the hippocampus as well as its microstructure and cell number. Stress may inhibit the hippocampal neuroregeneration as well as hippocampal neurogenesis and even induce neuronal death within the hippocampus. Diffusor tensor imaging (DTI) is a powerful method enabling the visualization of the microstructure integrity of white matter, to evaluate the changes (rate and directionality) of water diffusion within myelin tracts and provide enhanced images of white matter tracts compared to traditional MRI morphometry images. One can evaluate the differences in white matter using fractional anisotropy (FA), which is a scalar metric of the degree of anisotropy and diffusion direction of water molecules, indicating fiber density, mylination and axon diameter. Many studies report reduced gray matter volume caused by extreme stress or trauma in people both with the diagnosis of PTSD as well as stress-exposed non PTSD in comparison to healthy controls. Studies have revealed reduced volume mostly in the hippocampus but also in regions such as anterior cingulate, corpus callosum, insula, septum pellucidum, subcallosal cortex, amygdala, prefrontal cortex and total brain volume. The right hippocampus may be prone to the effect of stress much more than the left hippocampus. Moreover, comparing trauma-exposed non-PTSD and PTSD participants, they have found volumetric abnormalities only within the right hippocampus among the PTSD group. They suggest an additional pathological process underlying PTSD, connected with the right hippocampus volume.