Functional Neuroimaging Research in Posttraumatic Stress Disorder
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Springer-Verlag Tokyo 2006. All rights are reserved. Neuroimaging research in posttraumatic stress disorder (PTSD) is only two decadesold, but is rapidly expanding and evolving in methodological sophistication (Pitmanet al. 2001; Hull 2002; Liberzon and Phan 2003). Earlier structural and symptom-provocation studies are giving way to hypothesis-driven cognitive activationstudies, longitudinal and treatment studies, and translationally driven integrativestudies. The focused review of functional neuroimaging research in PTSD that followsdiscusses findings to better understand the functional neuroanatomy underlyingPTSD symptoms and pathophysiology. We begin with a selective review of theresearch on functional neuroanatomy of emotions that is specifically relevant toPTSD. The ensuing discussion links the two bodies of literature in order to providea better understanding of the processing of threat-related emotions and how this informsour understanding of the brain mechanisms that subserve PTSD.PTSD is characterized by exposure to life-threatening event/s associated withintense emotional reactions. Symptom clusters consist of reexperiencing the trauma(such as nightmares and intrusive memories), avoidance and numbing (avoidingtrauma-related cues, feeling emotionally distant from loved ones), and hyperarousal(hypervigilance, sleep disturbances) (American Psychiatric Association 2000). Becausethese criteria are descriptive, atheoretical, and not confined to a specific diagnosis,it is possible that patients with different neurobiological subtypes will sharethe same diagnosis or that patients with similar neurobiological abnormalities maycross descriptive categorical boundaries. Neurobiological evidence does offer thepotential to identify findings specific to trauma exposure and/or to PTSD's symptomsand pathophysiology, thereby helping to differentiate, define, and treat thesedisorders in a more meaningful way.One powerful, noninvasive means of investigating brain function in PTSD is theuse of relatively new neuroimaging methods such as magnetic resonance imaging(MRI) and positron emission tomography (PET). MRI methodology relies on spinproperties of protons in human brain tissue to outline brain structures and estimate their volume. Functional MRI (fMRI) uses the paramagnetic properties of oxy- anddeoxyhemoglobin in conjunction with rapid acquisition sequences to create maps ofblood-oxygen level dependent (BOLD) signal activity, i.e., blood flow reflective ofneuronal firing, thereby allowing the study of neural processing of specific tasks.Single photon emission computed tomography (SPECT) and PET use radio-emittingisotopes of biologically relevant molecules to estimate blood flow, metabolicrate, receptor binding, and quantification and the assessment of pharmacologicalactivity in vivo.
