Response-contingent stimulation. Biofeedback methods provide subjects with exteroceptive feedback (usually visual or auditory) of variations in some dimension of muscular, visceral or neural activity. The method is based on the (unproven) theory that VOLUNTARY MOTOR CONTROL depends On the integrity of a feedback loop that provides central motor control circuits with information about the activities of to-be-controlled effectors. Activities of deafferented STRIATE MUSCLES as well as those of the VISCERA and the nervous system that are difficult to detect, are resistant to voluntary control. In such cases, biofeedback is thought to facilitate control by augmenting the discriminability of the to-be-controlled activity and thereby enabling the subject to steer the otherwise undetectable and therefore non-voluntary effector activity towards a goal state identified by the feedback stimulus. Most frequently simple binary feedback is used in which a stimulus is presented when the criterion activity occurs and termi nates when the activity ceases to meet the criterion. Analog feedback has been used occasionally, for example by linking the position of a meter needle or the volume or pitch of a tone to such dimensions as the time integral of ELECTROMYOGRAM (EMG) activity, the level of diastolic blood pressure or the density of alpha ELECTROENCEPHALOGRAM (EEG) activity. However, it is not clear that analog feedback, which carries more information about effector activity, is more effective than binary feedback.
In the clinical realm, biofeedback is considered to be an ‘alternative medicine’ treatment and is employed as a means of generating control over a variety of primary disease symptoms. While its effectiveness remains controversial, proponents of the method argue that biofeedback is valuable in treating muscle tension HEADACHE, MIGRAINE headache, Raynaud’s disease, ANXIETY, irritable bowel syndrome, incontinence, chronic PAIN and INSOMNIA. Published evidence suggests that the method is most effective in the treatment of disorders that are expressed by a loss of muscular control including tension headache, incontinence and neuromuscular disorders. For other disorders, it is not clear that biofeedback offers therapeutic advantages over relaxation training.
Biofeedback was first popularized by J. Kamiya who published evidence in the early 1960s that when provided with auditory feedback, individuals could increase the prevalence of alpha-wave EEG. Typically, EEG at this frequency (about 10 Hz) is associated with a relaxed attentive state similar to that achieved in meditation.
At about the same time that Kamiya’s work appeared, H.Kimmel published evidence that the GALVANIC SKIN RESPONSE (GSR) could be influenced by response-contingent REINFORCEMENT. Kimmel’s demonstrations were not sufficiently powerful to overturn the received wisdom that autonomically mediated responses were immune to OPERANT CONDITIONING. However by emphasizing response-contingent reinforcement rather than feedback as the defining characteristic of the method, Kimmel cast the biofeedback problem within the more familiar conditioning framework. This stimulated a number of experimental studies that attempted to resolve the question of whether or not autonomically controlled responses were subject to operant conditioning. At the forefront of this experimental effort was a spate of studies that attempted to show that visceral control generated by response-contingent reinforcement was not a reflexive consequence of learned striate muscular control. From the mid 1960s to the early 1970s, a substantial experimental literature evolved on operant conditioning of visceral responses in curarized (see CURARE) animals. This work, which did much to promote the scientific respectability of biofeedback, purported to show that paralysed animals could be trained to produce highly specific visceromotor control. The implication of these demonstrations was that when provided with appropriate feedback, voluntary (or operant) control could be gained over non-voluntary activities. Subsequent work has shown that the phenomena reported in this early literature are not only fragile but of questionable theoretical significance.
Thus, there have been numerous failures to replicate the large effects demonstrated in the early literature. Furthermore, a strong experimental case has been made in support of the proposition that even when paralysed, animals could try to move their striate muscles and thereby generate neural outflow that influenced the visceral organs. Therefore, even if replicable, the curare experiments fail to prove that visceral control in curarized animals is independent of the neural processes that underlie voluntary control or operant conditioning of the striate (voluntary) muscles. Nevertheless, the curare experiments and other basic research that supported the development of biofeedback as a method have stimulated research into the roles of feedback in voluntary motor control and operant conditioning. Through its emphasis on the mediation of operant visceral control, it also refocused attention on the mechanisms in voluntary motor control. Finally biofeedback, which has rested on the idea that the voluntary control of an activity depends on the discriminability of that activity, has spawned research into the ability of individuals to detect variations in their own, mainly visceral, activities.
JASPER BRENER
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