How study of respiratory physiology aided our understanding of abnormal brain function in panic disorder

There is a substantial body of literature demonstrating that stimulation of respiration (hyperventilation) is a common event in panic disorder patient s during panic attack episodes. Further, a number of abnormalities in respi ration, such as enhanced CO2 sensitivity, have been detected in panic patie nts. This led some to posit that there is a fundamental abnormality in the physiological mechanisms that control breathing in panic disorder and that this abnormality is central to illness etiology. More recently, however, ev idence has accumulated suggesting that respiratory physiology is normal in panic patients and that their tendency to hyperventilate and to react with panic to respiratory stimulants like CO2 represents the triggering of a hyp ersensitive fear network. The fear network anatomy is taken from preclinica l studies that have identified the brain pathways that subserve the acquisi tion and maintenance of conditioned fear. Included are the amygdala and its brain stem projections, the hippocampus, and the medial prefrontal cortex. Although attempts to image this system in patients during panic attacks ha ve been difficult, the theory that the fear network is operative and hypera ctive in panic patients explains why both medication and psychosocial thera pies are clearly effective. Studies of respiration in panic disorder are an excellent example of the way in which peripheral markers have guided resea rchers in developing a more complete picture of the neural events that occu r in psychopathological states. (C) 2000 Elsevier Science B.V. All rights r eserved.