The vexing role of baseline: implications for neuroimaging studies of panic disorder

Imaging research has begun to transcend characterization of static anatomical relationships to localize neuronal substrates and identify brain physiologic processes involved in specific psychiatric disorders. While advances in imaging technology now provide a more direct window to the brain, interpretation of highly technical "functional imaging" measurements requires careful attention to baseline physiologic conditions that may reflect both state and trait-anxiety components of the disorder under investigation. Baseline anxiety and related physiologic alterations can substantially influence functional imaging measurements and their interpretation. Thus, it behooves the imaging researcher to take heed of lessons learned through systematic assessment of physiologic alterations when investigating disorders, such as panic disorder (PD), that have respiratory dysregulation as a core symptom. The focus of this paper is on how state and trait-anxiety characteristics of PD and related anxiety disorders, particularly anxiety effects on respiratory status, can influence imaging research findings. Examples from the panic imaging literature applying magnetic resonance spectroscopy, as well as an overview of baseline anxiety influences on functional MRI interpretation, are used to illustrate these considerations.