Brain Mapping: QEEG & Peak Agency

Allergy Pattern in the EEG

This paper describes an EEG pattern the author has found to be associated with an allergic response. A consistent 22 Hz frequency pattern has now been observed in more than 100 cases in recordings made with a bipolar (sequential) montage at F4-T4. Case illustrations with examples of this EEG pattern are provided.

The value of quantitative electroencephalography in clinical psychiatry: a report by the Committee on Research of the American Neuropsychiatric Association

The authors evaluate quantitative electroencephalography (qEEG) as a laboratory test in clinical psychiatry and describe specific techniques, including visual analysis, spectral analysis, univariate comparisons to normative healthy databases, multivariate comparisons to normative healthy and clinical databases, and advanced techniques that hold clinical promise. Controversial aspects of each technique are discussed, as are broader areas of criticism, such as commercial interests and standards of evidence. The published literature is selectively reviewed, and qEEG's applicability is assessed for disorders of childhood (learning and attentional disorders), dementia, mood disorders, anxiety, panic, obsessive-compulsive disorder, and schizophrenia. Emphasis is placed primarily on studies that use qEEG to aid in clinical diagnosis, and secondarily on studies that use qEEG to predict medication response or clinical course. Methodological problems are highlighted, the availability of large databases is discussed, and specific recommendations are made for further research and development. As a clinical laboratory test, qEEG's cautious use is recommended in attentional and learning disabilities of childhood, and in mood and dementing disorders of adulthood.

Treatment of Fibromyalgia Syndrome Using Low-Intensity Neurofeedback with the Flexyx Neurotherapy System: A Randomized Controlled Clinical Trial

Background. Treatment of fibromyalgia syndrome (FMS) remains a clinical challenge. Pain, somatic and cognitive symptoms may be due to neurosensitization involving CNS-activated autonomic and musculoskeletal reactions, associated with EEG abnormalities that may respond to brainwave-based stimulation biofeedback. This study's objective was to examine the efficacy and safety of a novel EEG neurobiofeedback treatment, the Flexyx Neurotherapy System® (FNS), and electrophysiological responses in persons with fibromyalgia. Methods. Arandomized, double-blind, placebo-controlled clinical trial was conducted in two private practices: a free-standing neurobiofeedback center and a rheumatologist's office at an academic medical center. Sixty-four participants with FMS (American College of Rheumatology criteria; Wolfe et al., 1990) for at least three years and symptoms for at least 48 months with no recent remission were randomized to treatment. A total of 22 treatment sessions were administered over at least 11 weeks of active (n = 33) or sham (n = 31) FNS therapy. Primary efficacy measures were the Clinical Global Impressions improvement scores, Clinician (CGI-I) and Participant (PGI-I) versions. Secondary outcomes included dolorimetry and tender point count, questionnaires (fibromyalgia symptom scales, CNS Dysfunction Questionnaire, Fibromyalgia Impact Questionnaire, Symptom Checklist-90-R), and EEG activity (delta, alpha, total amplitude). Results. More participants treated with active FNS than with sham improved partially or fully on the CGI-I at session 22 (p = .01) and follow-up (p = .04). The active FNS group had a higher CGI-I full response rate at session 22 (p < .05) but not at one-week post-treatment (p = .07). Significant active versus sham PGI-I responses were not detected (p>.10). There was no significant treatment effect on any secondary outcome measure and no specific symptom improved preferentially with active compared with sham FNS. The most commonly reported side effect was fatigue/tiredness. Pre-treatment delta/alpha EEG amplitude ratio > 1 was associated with PGI-I (but not CGI-I) response independent of treatment group assignment. Conclusion. FNS monotherapy is insufficient for treating chronic, nonremitting FMS.

The LENS (Low Energy Neurofeedback System): A Clinical Outcomes Study on One Hundred Patients at Stone Mountain Center, New York

Introduction. The Low Energy Neurofeedback System (LENS) developed by Dr. Len Ochs (2006a) uses feedback in the form of a radio frequency carrier wave, administered at a positive offset frequency from the person's own dominant EEG frequency. Although it is an unusual biofeedback procedure, the feedback being invisible and the subject passive, clinical evidence supports the efficacy of the LENS across a spectrum of conditions. Published research studies (Schoenberger, Shifflet, Esty, Ochs, & Matheis, 2001; Donaldson, Sella, & Mueller, 1998; Mueller, Donaldson, Nelson, & Layman, 2001) have shown the effectiveness of the LENS method with traumatic brain injury (TBI) and with fibromyalgia. No study to date has evaluated LENS treatment across the spectrum of disorders and with a significantly large sample. This study was devised to address these issues. The study hypotheses were that the LENS treatment would be effective in reducing both systematic symptom ratings and measurements of EEG amplitudes, and that the therapeutic effect would produce the most rapid improvements in early sessions of treatment. Method. "Blinded" research associates selected the first 100 patients from approximately 300 case files that met the following inclusion criteria: the person had received at least 10 treatment sessions, completed an initial CNS questionnaire, and that session-by-session subjective symptom ratings (SSRF) had been obtained. Patients ranged from 6 to 80 years old, almost evenly divided between male and female, with a wide range of symptoms and comorbid DSM-IV diagnoses. Results. Data were statistically analyzed for significance and corelational variables. Average symptom ratings across 15 major problem areas (e.g., anxiety, mood disturbance, attentional problems, fatigue, pain, sleep problems, etc.) showed significant improvements (p < .0001) from beginning to end of treatment. After an average of only 20 treatments the mean average of patient symptom ratings (0-10) declined from 7.92 to 3.96, a 50% improvement. Equally significant was the drop in EEG amplitude at the highest amplitude electrode site (HAS; p < .0001) as well as a lesser but still significant decrease at Cz (p < .002). A final analysis of the average symptom score with the HAS score showed them to be highly correlated. All hypotheses were confirmed. Conclusions. LENS treatment appears to be very efficient and effective in rapidly reducing a wide range of symptoms. It particularly produces rapid improvements in the first five to six sessions. Recommendations for future research are provided. Copyright © by The Haworth Press, Inc. All rights reserved.

Real-time functional MRI: development and emerging applications

Real-time functional magnetic resonance imaging (fMRI) is an emerging technique for assessing the dynamic and robust changes in brain activation during an ongoing experiment. Real-time fMRI allows measurement of several processes within the brain as they occur. The extracted information can be used to monitor the quality of acquired data sets, serve as the basis for neurofeedback training, and manipulate scans for interactive paradigm designs. Although more work is needed, recent results have demonstrated a variety of potential applications for real-time fMRI for research and clinical use. We discuss these developments and focus on methods enabling real-time analysis of fMRI data sets, novel research applications arising from these approaches, and potential use of real-time fMRI in clinical settings.

Clinical Database Development: Characterization of EEG Phenotypes

We propose development of evidence-based methods to guide clinical intervention in neurobehavioral syndromes based on categorization of individuals using both behavioral measures and quantification of the EEG (qEEG). Review of a large number of clinical EEG and qEEG studies suggests that it is plausible to identify a limited set of individual profiles that characterize the majority of the population. Statistical analysis has already been used to document “clusters” of qEEG features seen in populations of psychiatric patients. 1 These clusters are considered here as intermediate phenotypes, based on genetics, and are reliable indices of brain function, not isomorphic with DSM categories, and carry implications for therapeutic intervention. We call for statistical analysis methods to be applied to a broad clinical database of individuals diagnosed with neurobehavioral disorders in order to empirically define clusters of individuals who may be responsive to specific neurophysiologically based treatment interventions, namely administration of psychoactive medication and/or EEG neurofeedback. A tentative set of qEEG profiles is proposed based on clinical observation and experience. Implication for intervention with medication and neurofeedback for individuals with these neurophysiological profiles and specific qEEG patterns is presented.

Temporal Lobes and Their Importance in Neurofeedback

A review is presented on temporal lobe function and various conditions that are associated with the temporal lobes that have implications for both careful assessment and neurofeedback.

Exploring Hemispheric Differences in Infrared Brain Emissions

Background. Carmen (Toomim & Carmen, 1999) has shown that training to increase frontal lobe infrared emissions with neurofeedback techniques inhibits migraine pain, but nothing is known about the psychological correlates of the infrared signal. We assess if reading out loud would increase activation in the left hemisphere in comparison to the right. We also assessed test/retest reliability by repeating measures a week later. Methods. Measurements of infrared activity, while reading or not, were taken three times from the left, center, and right forehead of 24 persons who had signed Institutional Review Board approved consent forms. The order of reading and non-reading was varied systematically. Results. Significant differences in activation favoring the right rather than the left hemisphere were found, but only in those who read first. Both order-of-reading groups significantly declined in overall activity during the second session. Five of six Pearson correlations measuring test/retest reliabilities in the reading-first group and two of six in the reading-second group attained statistical significance. Only measurements taken at the left forehead site were reliable across all four conditions, which represent the combination of two orders and two types of stimulation. Conclusions. Test/retest correlations provide some support for the inference that the infrared measures reflect enduring traits, especially in the left hemisphere. Hemispheric difference data suggest that infrared emissions were sensitive to processes such as orientation, habituation and attention. There was no evidence of sensitivity to left hemisphere specialization for verbal processing.

Clinical utility of EEG in attention deficit hyperactivity disorder

Psychiatric research applications of electroencephalography (EEG), the earliest approach to imaging human cortical brain activity, are attracting increasing scientific and clinical interest. For more than 40 years, EEG research has attempted to characterize and quantify the neurophysiology of attention-deficit/hyperactivity disorder (ADHD), most consistently associating it with increased frontocentral theta band activity and increased theta to beta (θ/β) power ratio during rest compared to non-ADHD controls. Recent reports suggest that while these EEG measures demonstrate strong discriminant validity for ADHD, significant EEG heterogeneity also exists across ADHD-diagnosed individuals. In particular, additional studies validating the use of the θ/β power ratio measure appear to be needed before it can be used for clinical diagnosis. In recent years, the number and the scientific quality of research reports on EEG-based neurofeedback (NF) for ADHD have grown considerably, although the studies reviewed here do not yet support NF training as a first-line, stand-alone treatment modality. In particular, more research is needed comparing NF to placebo control and other effective treatments for ADHD. Currently, after a long period of relative stasis, the neurophysiological specificity of measures used in EEG research is rapidly increasing. It is likely, therefore, that new EEG studies of ADHD using higher density recordings and new measures drawn from viewing EEG as a 3-dimensional functional imaging modality, as well as intensive re-analyses of existing EEG study data, can better characterize the neurophysiological differences between and within ADHD and non-ADHD subjects, and lead to more precise diagnostic measures and effective NF approaches

Standards for the Use of Quantitative Electroencephalography (QEEG) in Neurofeedback: A Position Paper of the International Society for Neuronal Regulation

Background. This paper presents the findings of an interdisciplinary committee on standards for quantitative electroencephalography (QEEG) in neurofeedback which has been unanimously accepted by the International Society for Neuronal Regulation (ISNR) Board as a position paper of ISNR. Method. The committee reviewed current standards for quantitative encephalography in other specialties as well as scholarly literature on QEEG. Results. The panel reached the following conclusions: Although clinical research indicates that a full 19 channel QEEG does not appear necessary for conducting successful neurofeedback training, an increasing number of clinicians are using comprehensive QEEG evaluations to guide their neurofeedback training. An impressive body of peer reviewed scientific literature attests to the utility of the QEEG in providing a scientifically objective and clinically practical assessment of a wide range of psychiatric, psychological and medical conditions. Many of the significant contributions to the field of QEEG have come from psychologists and the Board of Professional Affairs of the American Psychological Association has concluded that QEEG is within the scope of practice of psychologists trained in this specialty. Unlike neurology and psychiatry, where QEEG is principally used for purposes of diagnosing medical pathology, neurotherapists who use QEEG primarily do so to guide EEG biofeedback training. It is not necessary for a physician to screen raw EEG data as part of a QEEG evaluation for neurofeedback training. Conclusions. For the purpose of encouraging high standards, recommendations are made for areas of training and study in this specialty, for certification, for equipment/software, and for procedures in data collection and analysis.

A Neurologist's Advice for Mental Health Professionals on the Use of QEEG and Neurofeedback

Neurofeedback and quantitative electroencephalography

This study was conducted in an attempt to determine the efficacy of neurofeedback (NFB) in the treatment of patients suffering from vertigo or tinnitus. Results indicated that after NFB, power for delta and theta bands was reduced; however, an increase of power was noted for the alpha bands. Furthermore, normalization was observed for the vestibular evoked potentials (VestEP). After NFB, a normalization of the VestEP was also demonstrated in a patient suffering from a bilateral tinnitus. A follow-up study (12 months after NFB) demonstrated that the VestEP were normal.

Optimal Functioning Training with EEG Biofeedback for Clinical Populations: A Case Study

Introduction. This case study of a mature female executive with Dissociative Disorder Not Otherwise Specified (DDNOS) demonstrates the Quality of Life Continuum (QLC) and the efficacy of specific EEG biofeedback protocols in enhancing performance and improving global life functioning for people with clinical disorders. The QLC begins with the functioning level of people with severe clinical problems and ends with superior functioning people, with three levels of functioning in between those two ends of the continuum. It is a graphic for demonstrating that any level of functioning can be improved through the use of protocols specifically designed for optimal functioning. Method. Pre- and post-quantitative electroencephalograms (QEEGs) were done on the subject. Other measures of change were self-report and co-worker feedback. The subject was taught how to train independently with specific peak performance protocols. She did 60 fifteen-minute training sessions in two months. Results. The changes in her QEEGs were measured by a comparison of her pre- and post-scores on the Thatcher Life Span EEG Reference Database. The subject went from 166 abnormalities with significance levels ranging from p < .025 to p < .001 to only 17 abnormalities. The subject reported significant life improvement changes, including increased energy and motivation. Among the changes cited by co-workers was a decrease in her anger outbursts from an average of three times per week to two times per month. Discussion. The independent use of neurofeedback with specific peak performance protocols can enhance the quality of life for a person with a clinical diagnosis.

Electrophysiology of Auditory Memory of Paragraphs Towards a Projection/Activation Theory of the Mind

Introduction: An investigation into the QEEG parameters of effective auditory memory for paragraphs was conducted employing sixty normal right-handed subjects. Method: Four stories were read to the subjects. The subjects engaged in an immediate thirty-second quiet recall period, which was followed by the subjects recalling the stories outloud. A delayed recalled assessment (about forty-five minutes) followed the same methodology. Results: The recall performances were correlated with the QEEG variables. For the input period the absolute levels of the Alpha coherence and phase generators from the left temporal lobe (T3), as well as the coherence Alpha (C3, P3, F7) were the predominant determinants of success in addition to F7 coherence Betal (13-32 Hz) and phase Betal from F8. Immediate recall was determined by the absolute levels of the projections from T3 (coherence and phase Alpha), symmetry Beta2 (32-64 Hz) at T3 and peak frequency of Betal at T5. Long-term recall was determined by the T3 generators (phase and coherence Alpha), F7 projections (phase Theta, coherence and phase Alpha, phase Betal, coherence Beta2), Fpl and F3 projections (coherence Beta2), and Fpl phase Betal. Degree of activation (from eyes closed) revealed additional variables relevant to success. Discussion: These research results are integrated into previous neuroscience research and implications for theories of brain function and neurotherapy applications are discussed.

An EEG Biofeedback Protocol for Affective Disorders

Conventional and quantitative electroencephalography in psychiatry

Electrical activity of each brain region is homeostatically regulated, resulting in predictable frequency composition of the background EEG. Replicated normative databases have established that the EEG power spectrum is independent of ethnic background. Artifact-free EEG evaluated relative to such norms displays few deviant values in healthy, normally functioning individuals. In subjects with psychiatric disorders, high proportions of abnormal findings have been reported with good concordance and high specificity and sensitivity across numerous studies, distinctive within a wide variety of disorders and often contributing to differential diagnosis and selection of treatment. New three-dimensional QEEG imaging methods offer an economical alternative to other functional brain imaging modalities.

Changes in EEG spectral power in the prefrontal cortex of conscious rats elicited by drugs interacting with dopaminergic and noradrenergic transmission

1. The electroencephalographic (EEG) effects of drugs interacting with dopaminergic and noradrenergic systems were studied in conscious rats. Power spectra (0 - 30 Hz) were recorded from electrodes implanted bilaterally in the prefrontal cortex. Drug effects on EEG power were calculated as the spectral power following drug administration divided by the spectral power after vehicle administration. 2. Dopaminergic agonists at low doses, (apomorphine 0. 01 mg kg-1 s.c., quinpirole 0.01 mg kg-1 i.p.) and dopaminergic antagonists (haloperidol 1 mg kg-1 i.p., raclopride 2.5 mg kg-1 s.c. ), which decrease dopaminergic transmission, induced an increase of EEG power. Conversely, dopaminergic agonists at higher doses (apomorphine 0.5 mg kg-1 s.c., quinpirole 0.5 mg kg-1 i.p.) which increase activation of postsynaptic D2 and D3 receptors, induced a decrease of EEG power. 3. The alpha1-adrenoceptor antagonists (phenoxybenzamine 0.64 mg kg-1 s.c., prazosin 0.32 mg kg-1 s.c.) and the alpha2-adrenoceptor agonists (UK 14304 0.05 mg kg-1 s.c., clonidine 0.025 mg kg-1 i.p.), which decrease noradrenergic transmission, induced an increase of EEG power. Conversely, the alpha1-adrenoceptor agonist, cirazoline (0.05 mg kg-1 s.c.), the adrenergic agent modafinil (250, 350 mg kg-1 i.p.) and alpha2-adrenoceptor antagonists (RX 821002 0.01 mg kg-1 s.c., yohimbine 0.5 mg kg-1 i.p.), which increase noradrenergic transmission, induced a decrease of EEG power. The effects of prazosin (0.64 mg kg-1 s.c.) were dose-dependently antagonized by co-administration with modafinil and cirazoline, but not by apomorphine. 4. In conclusion, pharmacological modulation of dopaminergic and noradrenergic transmission may result in consistent EEG changes: decreased dopaminergic or noradrenergic activity induces an increase of EEG spectral power; while increased dopaminergic or noradrenergic activity decreases EEG spectral power.

Preliminary evidence that daily changes in frontal alpha asymmetry correlate with changes in affect in therapy sessions

Frontal EEG alpha asymmetry was recorded from five depressed outpatients during early EEG biofeedback sessions. Mood was assessed prior to and after each session, and affect change scores were also derived by subtracting pre-session from post-session scores. Alpha magnitude was obtained via Fast Fourier Transforms. All scores (EEG alpha asymmetry and affect) were converted to deviation scores by subtracting each patient's daily score from that patient's mean across all available sessions for that patient. Pearson correlations were then computed between asymmetry and affect scores using the deviation scores combined over patients. There was little evidence of correlation between day-to-day asymmetry score and any single affect score. Strong correlations were obtained, however, between asymmetry score and affect change score and, in particular, between asymmetry score and change in positive affect.

Neurotherapy for stroke rehabilitation: A single case study

A 55-year-old male subject was treated with a two-tiered neurotherapy approach for a period of six months beginning approximately one year after a left-side CVA. Medical evaluation revealed left posterior temporal/parietal infarctions secondary to occlusion of the left internal carotid artery. The patient complained of hesitant speech with word finding difficulty and paraphasia, difficulty focusing his right eye, lack of balance and coordination, poor short-term memory, poor concentration, anxiety, depression, and tinnitus. A quantitative electroencephalograph (QEEG) analysis revealed increased left-side 4–7-Hz activity and alpha persistence on eye opening. Two neurotherapy approaches were used beginning with electroencephalographic entrainment feedback (EEF). This was followed by neurofeedback to inhibit 4–7 Hz and increase 15–21 Hz over sensorimotor and speech areas. At the conclusion of treatment there were significant reductions in slow-wave activity. Improvement was evident in speech fluency, word finding, balance and coordination, attention, and concentration. Depression, anxiety, and tinnitus were greatly reduced.

Spectral coherence in normal adults: unrestricted principal components analysis; relation of factors to age, gender, and neuropsychologic data

This paper demonstrates, by means of Principal Components Analysis (PCA), an objective approach to the reduction of large data sets produced by multichannel spectral coherence analyses. Coherence data, gathered from 371 normal healthy adults using Hjorth/Laplacian referencing during waking eyes-open and eyes-closed states, were analyzed by "unrestricted" PCA where neither spatial nor temporal variance was folded into among subject variance. There was substantial data reduction with our 4416 initial coherence variables for each state reduced to just 150 factors containing approximately 80% of the variance reflecting a 30 fold concentration of information content. Varimax rotation of the first 40 factors, encompassing 50% of the total variance for both states, revealed loading patterns primarily bilateral with no hemispheric bias, relationships primarily between distant single electrode pairs, (although a single electrode to multiple electrode pattern was also observed), and involvement of all spectral bands. Elemental left to right and anterior to posterior coherence patterns, often used on an a priori basis for coherence studies, were not evident among the rotated factor loading patterns. On the basis of high loadings upon extra bipolar artifact channels, 32 factors accounting for approximately 40% of the variance were identified as reflecting artifactual coherence relationships. By multiple regression the 48 non-artifactual factor scores successfully predicted subject age. In general, coherence diminished with age, which may partly explain age-related EEG desynchronization in healthy adults. Coherence factors also predicted 6 of 10 neuropsychologic variables. Gender was successfully predicted by discriminant analysis. No global interpretations about coherence and gender or neuropsychologic function were possible, i.e., almost equal numbers of factors increased as decreased in males as females. PCA derived coherence factor scores are useful for subsequent statistical analyses, but their factor loading plots of cortical coupling may require more experience to fully interpret.

Psychometric Properties of Resting Anterior EEG Asymmetry: Temporal Stability and Internal Consistency

Test-retest reliability in EEG frequency analysis

This study was performed to gain a better understanding of EEG frequency analysis test-retest reliability in normal healthy adults, and to evaluate factors which could influence the measured inter-record differences. Nineteen subjects underwent serial EEG recordings at 5 min and 12–16 week intervals. Records were visually edited using a standardized protocol, and FFT frequency analysis performed on segments of 60, 40, or 20 sec total length. Correlation coefficients for broad band features averaged 0.92 over the 5 min retest interval and 0.84 over the 12–16 week interval. There was essentially no difference between correlation coefficients of absolute and relative power features. Coefficients based on 60 sec records were marginally higher than those of 40 or 20 sec records. On the other hand, test-retest percent differences were typically lower for relative as opposed to absolute power features, and 60 sec records showed consistently lower percent differences than did 40 or particularly 20 sec records. Peak alpha frequency and mean frequency were the most stable EEG features at either interval. Montage had significant effects on test-retest differences at the 12–16 week interval. A significant association between intra-record and inter-record variability could not be demonstrated.

The effects of electrode placement upon EEG biofeedback training: the monopolar-bipolar controversy

Roles of tradition, convenience, and noise or artifact rejection are discussed with regard to the monopolar versus bipolar electrode placement controversy in electroencephalography (EEG). Particular emphasis is placed on the relevance to biofeedback. The crucial interactions between the differential amplifier, brain waves, and monopolar/bipolar placements are discussed. Through logical analysis and empirical observation, it is demonstrated how the very nature of the EEG's differential amplifiers must destroy those elements of brain activity which are common to the recording electrodes. Controlled experiments further illustrate the critical importance of electrode placements. Various methods, including preferred electrode placements, are presented to help resolve recording problems that frequently arise. It is concluded that there are serious implications for researchers, EEG clinicians, biofeedback providers, and their clients in preferring one type of electrode placement technique over the other. EEG recording accuracy is affected by this choice.

EEG Measures of Cerebral Asymmetry: Conceptual and Methodological Issues

An overview of the use of EEG to assess hemispheric differences in cognitive and affective processes is presented. Some of the advantages of using EEG to assess asymmetric hemispheric differences in the study of complex mental activity are described. Following this brief introduction, two conceptual issues which are central to studies of EEG asymmetries are introduced: (1) the distinction between hemispheric specialization and activation, and (2) the importance of rostral-caudal differences for the understanding of both specialization and activation. Three methodological issues in the use of EEG to assess hemispheric differences are then presented: (1) the use of asymmetry metrics, (2) muscle artifact, and (3) appropriate reference electrode location. Finally, some empirical examples of using EEG to assess affective and cognitive processes which illustrate these conceptual and methodological issues are described.

Test-retest reliability of spectral parameters of the EEG

The topic of this paper is the intraindividual stability of the EEG at rest for repeated recordings with respect to two sets of spectral parameters. Variability arises due to changes in experimental conditions (such as vigilance) and also due to the inherent random elements of the EEG. The two sets of parameters considered are broad-band parameters and parameters characterizing rhythmic and ‘diffuse’ activity separately, derived from autoregressive fitting. In spite of some imprecision in the definition of the EEG at rest, satisfactory test-retest correlations were found. They proved to be quite homogeneous topographically, but not across frequency bands: delta power is less reliable and to some extent also beta activity, whereas the alpha bands perform well. The frequency of the alpha rhythm shows a good reliability and, given the difficulties involved with the concept, also the degree of synchronization. The power of rhythmic and of diffuse activity showed more modest retest correlations, probably to be attributed to methodological problems in determining these quantities. On the whole, the results confirm that the normal EEG can be treated as an intraindividually rather stable trait, that artifacts play a minor role in this respect and that 20 sec of activity are sufficient to reduce adequately the variability inherent in the EEG. Résumé Le sujet de cet article est la stabilité intra-individuelle de l'EEG de repos lors d'enregistrements répétés, ceci à partir de deux ensembles de paramètres spectraux. L'augmentation de la variabilité est due à des modifications des conditions expérimentales (telles la vigilance) ainsi qu'aux éléments aléatoires inhérents à l'EEG. Les deux ensembles types de paramétres considérés sont les paramètres de bande large et ceux individualisant une activité rythmique et diffuse à partir d'une évaluation autorégressive. En dépit de quelques imprécisions dans la définition de l'EEG de repos, des corrélations entre tests renouvelés satisfaisantes ont été trouvées. Elles se sont montrées tout à fait homogènes topographiquement, mais non entre bandes de fréquences: la puissance delta est moins fiable et dans une certaine mesure, l'activité bêta, alors que pour la bande alpha les résultats sont bons. La fréquence du rythme alpha présente une bonne fiabilité ainsi que son degré de synchronisation compte tenu des difficultés mêmes qu'offre cette notion. La puissance de l'activité rythmique et diffuse a apporté des corrélations plus modestes entre tests, probablement à cause de problèmes méthodologiques de détermination de ces quantités. En somme, ces résultats confirment le fait que l'EEG normal peut être traité comme une caractéristique intra-individuelle plutôt stable, que les artéfacts ne jouent à cet égard qu'un rôle mineur et que 20 sec d'activité sont suffisantes pour réduire de façon acceptable la variabilité inhérente à l'EEG.

Biofeedback produced slow brain potentials and task performance

Twenty subjects learned to control slow potential (SP) shifts of the brain by means of a biofeedback procedure. Depending upon the pitch of a signal tone, negative SP shifts had to be increased or reduced during intervals of 6 sec each. Visual feedback of the actual SP shift was given. Blocks of training trials alternated with blocks of test trials without any feedback of the SPs. At the end of every test trial a simple arithmetic problem had to be solved by the subjects. Subjects performed the computation in a shorter time interval if an increased negativity preceded task onset as compared to slower response times during suppression of negativity. Results suggest that cortical negativity reflects unspecific preparation for cerebral performance.