Investigating the pathogenesis of posttraumatic stress disorder with neuroimaging

Rapidly evolving brain neuroimaging techniques such as magnetic resonance i maging (MRI) and positron emission tomography (PET) Eire proving fruitful i n exploring the pathogenesis and pathophysiology of posttraumatic stress di sorder (PTSD). Structural abnormalities in PTSD found with MRI include nons pecific white matter lesions and decreased hippocampal volume. These abnorm alities may reflect pretrauma vulnerability to develop PTSD, or they may be a consequence of traumatic exposure, PTSD, and/or PTSD sequelae. Functiona l neuroimaging symptom provocation and cognitive activation paradigms using PET measurement of regional cerebral blood flow have revealed greater acti vation of the amygdala and anterior paralimbic structures (which are known to be involved in processing negative emotions such as fear), greater deact ivation of Broca's region (motor speech) and other nonlimbic cortical regio ns, and failure of activation of the cingulate cortex (which possibly plays an inhibitory role) in response to trauma- related stimuli in individuals with PTSD. Functional MRI research has shown the amygdala to be hyperrespon sive to fear-related stimuli in this disorder. Research with PET suggests t hat cortical, notably hippocampal, metabolism is suppressed to a greater ex tent by pharmacologic stimulation of the noradrenergic system in persons wi th PTSD. The growth of knowledge concerning the anatomical and neurochemica l basis of this important mental disorder will hopefully eventually lead to rational psychological and pharmacologic treatments.