Biofeedback is best understood as a closed feedback loop consisting of a person or other animal, a response, a means to detect the response, and a mechanism for displaying the response to the person or animal—the response is thus fed back. For example, a person can be instructed to increase his or her heart rate; the heart rate is displayed by a monitor and fed back to the person; a feedback loop is thereby established. Biological systems have numerous, reflexive feedback loops to maintain homeostatic integrity—for example, body temperature, blood sugar, blood pressure, and endocrine levels. Fluctuations are kept within narrow limits by such feedback loops. However, biofeedback learning is not reflexive; it is more closely associated with higherorder learning processes.
One motive for the development of biofeedback was to devise therapies for volitional control over processes considered automatic and reflexive. Processes such as heart rate, blood pressure, and gastric secretion change along their respective dimensions, depending upon metabolic needs and emotional states. But when such processes move beyond certain limits, then health and proper functioning of the organism become compromised. Biofeedback self-regulation, as a therapy, can be viewed as a learning technique to help keep systems within proper limits with little of the side effects of more traditional medical therapies. A second stimulus for biofeedback development came from theorists concerned with disproving the hypothesis that responses innervated by the autonomic nervous system were not modifiable by reward learning. This position held that such responses were capable of being modified only through the conditional response techniques crafted by I. P. Pavlov.
A third reason for exploration came from interest in the self-control of conscious states. The fact that electroencephalograph^ (EEG) rhythms might be modifiable by providing information to an observer regarding EEG activity led to increased biofeedback research. Finally, the idea that self-regulation of neuromuscular function might help alleviate certain types of pain, such as headache, or lead to recovery of muscular function following trauma or disease, further helped the development of biofeedback.
Early experimental reports indicated that human subjects could control vasomotor responses, electrodermal activity, and heart rate. In the first of these studies a Russian investigator, Lisina (in Razran), claimed that when individuals were allowed to view a polygraph displaying their vasomotor responses to electric shock, they learned to produce vasodilation to escape the shock—the usual response to cutaneous electrical stimulation is vasoconstriction. Following these early studies, a number of laboratories began publishing data claiming to have effected reward learning in a variety of autonomically mediated responses with both humans and animals. Besides the usual methodological objections, criticism centered on the mechanisms responsible for the learning. A mediation issue was proposed that held that true reward learning was not occurring. Instead, it was argued, the subjects were somehow mediating the auto-nomic response through either cognition (i.e., thinking either calming or emotional thoughts) or covert striate muscular activity (either intended, with no movement, or actual, with movement). Although this issue remains unresolved, studies on subjects paralyzed by spinal lesions and plagued by hypotension indicated that neither cognitions, small muscular twitches, nor actual movement could account entirely for the biofeedback-produced changes. Autonomic reward learning is also influenced by such variables as type of feedback, awareness, instructions, homeostatic restraints, and links between somatic and autonomic response systems.
Biofeedback has been applied to athletic performance, Raynaud's disease, cardiac abnormalities, migraine headache, functional diarrhea, tension headache, temporo-mandibular disorder, essential hypertension, diabetes mel-litus, Attention-Deficit/Hyperactivity Disorder, gait disorders, urinary incontinence, nocturnal enuresis, irritable bowel syndrome, tinnitus, fibromyalgia, and asthma, as well as to other problems with autonomic involvement such as anxiety, eczema, and sexual arousal. The applications continue to expand, and biofeedback is, in fact, the method of choice in treating Raynaud's disease.
The application of biofeedback techniques to problems resulting from neuromuscular dysfunction has shown considerable promise. Many reports are available on a wide array of disorders, ranging from headache to foot drop. Neu-romuscular feedback has shown impressive specificity of control by successfully training subjects to either activate or inhibit activity of single motor muscle units as well as to control fecal incontinence.
Attempts have been made to modulate EEG activity through either biofeedback or manipulation of cognitive states thought to underlie a specific range of EEG frequencies. Results of these studies showed that biofeedback for alpha (8-12 Hz) did change and was accompanied by changes in psychological state. Increased alpha was related to feelings of relaxed attention and absence of anxiety. Whether increases in alpha produced psychological changes or the psychological states produced the EEG changes became part of the mediation issue. Evidence available strongly implicates the role of eye movement in the production or suppression of alpha, and this oculomotor hypothesis is the most salient explanation regarding alpha control. Convergence, divergence, and focusing of the eyes are related to the amount of alpha produced. In addition, correlated psychological states with such changes are at least partly due to expectations. Attempts have also been made to relate theta EEG (4-7 Hz) to the psychological states of dreamlike imagery and creative insight. Finally, some research has focused on modification of the sensori-motor rhythm (12-14 Hz) to reduce epileptic seizures. Results showed that when modification occurred in the 6-8-Hz band there was a concomitant reduction of seizures.
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