Brief summary of evidence supporting the efficacy of biofeedback for abnormal levels of anxiety:
Yucha and Gilbert (2004) report that "very few well- controlled, randomized studies have shown biofeedback to be superior to other relaxation and self-control methods for reducing anxiety. Most show biofeedback (EMG, GSR, thermal, or neurofeedback) to be roughly equivalent to progressive relaxation or meditation. Two studies showed biofeedback's efficacy in reducing anxiety without making comparisons with other relaxation techniques. Hurley and Meminger (1992) used frontal EMG biofeedback with 40 subjects trained to criterion and assessed anxiety over time using the State-Trait Anxiety Inventory (STAI). State anxiety improved more than trait anxiety. Wenck, Leu, and D'Amato (1996) trained 150 7th and 8th-graders with thermal and EMG feedback, and found significant reduction in state and trait anxiety. Roome and Romney (1985) compared progressive muscle relaxation to EMG biofeedback training with 30 children and found an advantage for biofeedback; Scandrett, Bean, Breeden, & Powell (1986) found some advantage of progressive muscle relaxation over EMG biofeedback in reducing anxiety in adult psychiatric inpatients and outpatients. Vanathy, Sharma, and Kumar (1998), applying EEG biofeedback to generalized anxiety disorder, compared increased alpha with increased theta. The two procedures were both effective in decreasing symptoms.
Rice, Blanchard, and Purcell (1994) studied reduction in generalized anxiety by comparing groups given EMG frontal feedback, EEG alpha-increase feedback, EEG alpha- decrease feedback, a pseudo-meditation condition, and a wait-list control. All treatment groups had comparable and significant decreases in the STAI as well as drops in Psychosomatic Symptom Checklist. Similar results were obtained by Sarkar, Rathee, and Neera (1999) by comparing the generalized anxiety disorder response to pharmacotherapy and to biofeedback; the two treatments had similar effects on symptom reduction. Hawkins, Doell, Lindseth, Jeffers, and Skaggs (1980), concluded from a study with 40 hospitalized schizophrenics that thermal biofeedback and relaxation instructions had equivalent effect on anxiety reduction. Fehring (1983) found that adding GSR biofeedback to a Benson-type relaxation technique reduced anxiety symptoms more than relaxation alone."
* Much of the information provided here is from Carolyn Yucha and Christopher Gilbert's 2004 book "Evidence Based Practice in Biofeedback & Neurofeedback" AAPB, Wheat Ridge, CO.