According to some studies, 80% of subjects suffering from post-traumatic stress disorder (PTSD) present twice the risk of developing an insanity as they age because of the high level of stress that has been induced. Indeed, the triggered trauma has a deleterious effect on the establishment of the stress’ axis (the hypothalamic pituitary adrenal axis) which is then not able to regulate itself. As a consequence, the hippocampal neurons will be attacked by an excess of cortisol. Memory's dysfunction is central in the symptomatology of PTSD, particularly in respect to encoding and recall. The hippocampus is able to transfer information to the prefrontal cortex. Actually, subjects with PTSD present less activity in the prefrontal cortex triggered by a decrease of encoding and recall capacities. EMDR therapy (eye movement desensitization and recruitment) allow for a fast relief of symptoms by a bilateral alternate stimulation (SBA). Indeed, saccadic eye movements stem affect related to the traumatic event and process the associated cognitions. During the desensitization phase in EMDR, we noticed an increase in activity of the brain's prefrontal, ventromedial, amygdala and thalamic regions. Indeed, the recall of traumatic memories goes through implicit emotional valence regions and associative areas for which the experience is already deeply integrated. After comparing cerebral activity before and after the therapy, researches on EMDR shows that a reduction of stress’ symptoms has some sensitive link to PTSD (in prevention to dementia).