Neuroimaging Findings in Anxiety Disorders

Individuals with severe anxiety have long sought a physical basis for their symptoms. There is increasing evidence to suggest brain abnormalities as the primary mechanism responsible for pathological anxiety, particularly panic disorder. However, older-generation brain imaging techniques, capable of assessing brain structure, have not identified consistent anatomical differences or structural abnormalities by which to explain the symptoms. In this regard, the development of modern functional imaging techniques that can specifically assess regional brain blood flow, metabolic status, or chemical composition are beginning to elucidate underlying brain mechanisms which may be responsible for "state" or situational-specific anxiety and "trait" or pathological anxiety. The intent of this article is to provide a review of neuroimaging studies undertaken to investigate state anxiety or specific anxiety disorders. The focus of this article is on studies that have used newer brain imaging techniques capable of assessing brain functionality, such as single photon emission computerized tomography, positron emission tomography, or magnetic resonance spectroscopy (MRS), in relationship to specific anxiety disorders. We have undertaken studies of panic disorder using MRS to investigate acute panic precipitated by physiological or chemical challanges, such as intravenous sodium lactate infusion, while measuring brain metabolic responses. These studies are presented in detail as a model of how these newer functional imaging modalities can be applied as a tool to begin to unravel the underlying pathophysiological processes responsible for production of panic. It is anticipated that future application of these newer functional imaging techniques will allow both the determination of a brain mechanism(s) responsible for pathological anxiety and advance our understanding of mechanisms responsible for effective treatments.