Investigating the Pathogenesis of Posttraumatic Stress Disorder With Neuroimaging

Rapidly evolving brain neuroimaging techniques such as magnetic resonance imaging (MRI) andpositron emission tomography (PET) are proving fruitful in exploring the pathogenesis and pathophysiologyof posttraumatic stress disorder (PTSD). Structural abnormalities in PTSD found withMRI include nonspecific white matter lesions and decreased hippocampal volume. These abnormalitiesmay reflect pretrauma vulnerability to develop PTSD, or they may be a consequence of traumaticexposure, PTSD, and/or PTSD sequelae. Functional neuroimaging symptom provocation and cognitiveactivation paradigms using PET measurement of regional cerebral blood flow have revealedgreater activation of the amygdala and anterior paralimbic structures (which are known to be involvedin processing negative emotions such as fear), greater deactivation of Broca’s region (motor speech)and other nonlimbic cortical regions, and failure of activation of the cingulate cortex (which possiblyplays an inhibitory role) in response to trauma-related stimuli in individuals with PTSD. FunctionalMRI research has shown the amygdala to be hyperresponsive to fear-related stimuli in this disorder.Research with PET suggests that cortical, notably hippocampal, metabolism is suppressed to a greaterextent by pharmacologic stimulation of the noradrenergic system in persons with PTSD. The growthof knowledge concerning the anatomical and neurochemical basis of this important mental disorderwill hopefully eventually lead to rational psychological and pharmacologic treatments.