Biofeedback refers to the operant training of physiological responding. Variants include electromyography (EMG), electrodermal activity (EDA), skin temperature, heart rate (HR) and heart rate variability (HRV), respiratory biofeedback of end-tidal CO2 (ETCO2), electroencephalography (EEG) signal, and blood oxygen-level dependent signal using functional magnetic resonance imaging (fMRI). This chapter presents a qualitative and quantitative systematic review of randomized controlled trials of biofeedback for anxiety disorders as defined by the 3rd through 5th editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM). Meta-analytic results indicated that biofeedback (broadly defined) is superior to wait list, but has not been shown to be superior to active treatment conditions or to conditions in which patients are trained to change their physiological responding in a countertherapeutic direction. Thus, although biofeedback appears generally efficacious for anxiety disorders, the specific effects of biofeedback cannot be distinguished from nonspecific effects of treatment. Further, significant limitations were identified in the existing literature, with the majority receiving a "weak" rating according to Effective Public Health Practice Project (EPHPP) rating system guidelines. Future directions for research are discussed.
Keywords: Anxiety; Biofeedback; Neurofeedback; Panic; Phobia; Psychophysiology.