As is evident from other articles of this text, the twentieth century saw major advances in knowledge of the functioning of the human brain. Many such advances were associated with technological developments in computer science and brain imaging techniques, such as functional magnetic resonance imaging (fMRI), and with developments in psychopharmaco-logical treatments in psychiatry. Similarly, twentieth century advances in the cognitive sciences have been associated with the development of effective cognitive and behavioral therapies for mental disorders and cognitive rehabilitation techniques for acquired brain damage. However, despite the many advances, treatment of psychiatric type disorders still primarily involves temporary control of the symptoms rather than permanent change in the underlying neurophy-siology or actual cure. Pharmacological treatments have unwanted and often dangerous side effects,

Encyclopedia of the Human Brain Volume 3

Copyright 2002, Elsevier Science (USA).

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whereas behavioral changes resulting from behavior modification procedures often fail to generalize to a sufficiently wide range of life situations, and cognitive rehabilitation has had limited success in many cases of traumatic brain injury. Furthermore, some neurophy-siological diseases such as Alzheimer's disease have responded to treatment only marginally. Obviously, the need remains for new and/or improved treatment procedures for disorders now known to have neuro-physiological bases (or correlates). Many alternative treatments have been proposed, with advocates of each claiming positive effects on neurophysiological function, e.g., biofeedback, chiropractic care, music therapy, meditation. This article is about one of the more recent ones: neurofeedback (NF) (sometimes referred to as neurotherapy or EEG biofeedback). Biofeedback may be defined generally as a research or clinical treatment technique in which electronic equipment presents a person with information about ongoing physiological processes that otherwise could not be monitored readily, thus allowing the person to learn through operant conditioning to self-regulate those processes. NF is a specific case ofbiofeedback in which the physiological process involved is the electrical activity of the brain.

Due in part to the newness of NF as a treatment modality, there is considerable controversy regarding which topics are of most importance to the field. Topics selected for inclusion in this article and many of the ideas presented are based on the author's 30 years of following developments in EEG biofeedback and several years of experience with NF in a part-time private practice in clinical psychology. The content also is based in part on the author's experiences in co-editing, with Andrew Abarbanel, the text Introduction to Quantitative EEG and Neurofeedback, and in part on the results of a survey questionnaire concerning the current status of NF returned to the author by 10 of today's leading NF practitioners. Hopefully, this article presents an accurate overview of the field of NF as it exists at the beginning of the twenty-first century. The author, however, assumes sole responsibility for the content, which may be perceived by some as neglecting certain important topics and misrepresenting or overemphasizing others.

A. Procedures and Premises

In the practice of clinical NF, a client requesting treatment first is evaluated to determine whether NF is an appropriate primary or adjunctive treatment mod ality. This involves considerations such as specific symptoms, likelihood of motivation and ability to persist in attempting to modify his or her EEG over the usual 20-50 sessions required for optimal results, use of prescribed (or illegal) pharmacological agents, and co-existing and contraindicative psychosocial, environmental, psychiatric, and/or general medical problems (e.g., certain types of seizures) for which a referral for mental health and/or medical treatment is needed. To obtain this information and other data that may be used for pre- and posttreatment comparisons in evaluating progress and outcome, practitioners often use structured interviews, behavior rating scales, and various standardized psychological tests such as continuous performance tests. Many NF practitioners also require an EEG assessment prior to beginning treatment. This most often involves a quantified (quantitative) EEG (QEEG) evaluation and comparison of obtained measures of wave frequency, amplitude, phase relationships, and coherence between scalp electrode sites to a lifespan database to determine which, if any, are abnormal and, hence, candidates for attempting normalization through NF.

Actual treatment begins once a client is considered acceptable for this type treatment and the EEG parameters to be modified are decided upon. An electrode (or more than one electrode in some applications) is placed at an appropriate scalp location, the EEG activity emanating from that location is filtered and amplified, and a feedback signal is presented to the client reflecting the current status of a selected feature (or features) of the ongoing EEG. The EEG activity actually eliciting the feedback varies with equipment. After filtration and amplification, some equipment provides a direct analogue or digital representation of the raw EEG in the feedback. Most often, however, the raw EEG signal is averaged over short periods of time (epochs) and a Fourier analysis is made for each epoch. It is these averaged and transformed data that are reflected by the feedback.

NF clinicians vary in their rationale for selecting a specific scalp electrode site(s) for training. Some train at sites from the international 10-20 electrode system where QEEG abnormalities were greatest for the client, whereas others regularly use specific sites identified through their clinical experience (or the experiences of others) to be the most effective for specific conditions, e.g., Cz for attention problems. Feedback usually is auditory (tones varying in pitch and/or volume) or visual (e.g., moving colored bars, puzzles, or animations are presented on a computer monitor). With most modern equipment, feedback possibilities are nearly endless considering all the possible pitch, volume, and visual stimulus combinations. Various combinations usually are tried during early sessions until one considered acceptable to the client is agreed upon. Most often, feedback is given for desired changes in the amplitude of specific EEG frequency bands (or duration of specified frequency amplitudes) over the course of a training session, e.g., for changes in commonly used EEG frequencies such as d (0.5-4 Hz), 6 (4-8 Hz), a (8-12 Hz), sensorimotor rhythm (12-15Hz) and/or b (> 12Hz bands). In some treatment protocols, feedback is provided to facilitate increased amplitude in one frequency band and simultaneous decreases in another, e.g., increase b-decrease 6. Although wave amplitude is the EEG characteristic presently involved most often in NF, degree of coherence, i.e., correlation and similarity of waveform morphology, phase lag, i.e., transmission time in milliseconds, between two (or more) scalp electrode sites, and various other EEG measures increasingly are being used. As with electrode site selection, there is considerable variability in the rationale for selecting a specific EEG feature for feedback. Some practitioners base selection on QEEG findings on the individual client, whereas others regularly use "canned" protocols based on clinical lore regarding what is effective for a given condition. Modern NF equipment also monitors EEG artifacts such as those caused by eye or other body movements or muscle tension (electromyogram or EMG) and inhibits feedback when such artifacts are above a level preset by the neurotherapist. Thus, feedback is provided only when the client's target EEG feature is changing above (or below) a desired threshold and artifacts are below a preset inhibit level. Typically, a cumulative score is kept of the percentage of time that the client received feedback during a session. Neuro-therapists generally agree that, for optimal learning, thresholds and artifact inhibit levels should be set so that the client is able to meet all criteria and, thus, obtain feedback 70-80% of the time. As learning occurs, thresholds and inhibit levels may be made increasingly challenging. There is general agreement that training sessions should occur 2-3 times per week, especially during the earlier and middle portions of the total treatment.

The basic premises of NF, in many respects, are quite simple:

1. Functioning of the central nervous system is electrochemical in nature. It is commonly accepted that changes in neurochemistry can result in changes in behavior, perception, emotions, and cognition. It is logical to assume that changes in electrophysiology (i.e., EEG activity) also can result in such changes.

2. If an appropriately motivated person is provided immediate, accurate feedback regarding aspects of his or her ongoing brain electrical activity (EEG), he or she can learn to regulate it, i.e., operant conditioning of the EEG activity can occur.

3. If such operant learning is repeated a sufficient number of times, the electrophysiological changes will become quite stable.

4. Appropriate stable changes in brain electrophysiol-ogy can result in relatively permanent positive changes in perceptual, cognitive, and behavioral functioning across various settings and activities of daily life.

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