**1. Introduction**

One in two people will be exposed to a life‐threatening trauma event in their life [1]. Prolonged stress results in neuroendocrine deficiency axis and defensive mechanisms are weakened, and stress hormones are activated. Definition of neuroanatomical or morpholog‐ ical substrate is crucial in defining any condition, illness or disorder in medicine and

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

psychiatry. There is almost no area of the brain that is not directly or indirectly affected by the stress or trauma impact [2–5]. The field of neuroimaging has made tremendous advances in the past decade and has contributed greatly to our understanding of post‐traumatic stress disorder (PTSD). Recent neuroimaging investigations have shown significant neurobiological changes in PTSD. The areas of the brain that are different in patients with PTSD compared to those in control subjects appear to be: hippocampus, amygdala, and prefrontal cortex. The amygdala appears to be hyperreactive to trauma‐related stimuli. The hallmark symptoms of PTSD may be related to a failure of higher brain regions to dampen the exaggerated symptoms of arousal and distress that are mediated through the amygdala in response to reminders of the traumatic event [6–8]. The findings of structural and functional neuroimaging studies of post‐traumatic stress disorder are reviewed as they relate to our current understanding of this disorder. Some volumetric investigations show that some other subcortical brain structures are also involved in trauma impact such as caudate nucleus, putamen [9–11].
