SEARCH · PubMed Health

Results for “Alpha Rhythm”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

PubMedDate not supplied

[Fractal diagnostics of disturbances in the alpha-rhythm dynamics in patients with epilepsy].

A new method for analyzing the chaotic component of EEG is proposed. The method is based on estimating the fractal dimension of fluctuations of alpha-rhythm power (the square of amplitude). It is shown that the dimensions of the background EEG fragments for epilepsy patients is significantly higher than that in norm, indicating a disbalance of cerebral mechanisms that control the alpha-activity in this disease. A tendency toward the disturbance of the normal fractal structure of EEG in a group of patients with initial signs of epilepsy was revealed. This suggests that the method is of considerable promise for setting the individual long-term prognosis of the development of the epileptic syndrome.

Alpha Rhythm↗

PubMed1985

Asymmetry of occipital alpha-rhythm under resting conditions: a neurophysiological measure of "hemisphericity".

Using the resting EEGs of 20 healthy subjects in semirecumbent position with eyes closed and left undisturbed, we studied the question whether and, if so, to what extent, lateralization of occipital alpha-rhythm depends on level of vigilance. As a simple indicator of vigilance, the relative alpha-power for each 2-sec. epoch of 02-CZ (occipital right) was calculated. Lateralization was defined as the ratio of absolute alpha-powers in 01-CZ and 02-CZ (occipital left and right). This was also calculated epoch by epoch. The results of individual analysis of data from each subject allowed categorization into 3 types. This typological differentiation obtained quantitatively could be supported by visual pattern analysis. The findings are discussed in relation to the state- vs trait-problem which constantly confronts us when we interpret experimentally obtained functional asymmetries of hemispheres.

Adult↗

PubMed1978

[Statistical spectral study of alpha rhythms: modifications due to the tardive action of a hypnotic (author's transl)].

In a simple blind study to evaluate electroencephalographic criteria objectively, and to continue characterization of psychotropic compounds, 5 mg of nitrazepam, a hypnotic derivative, was given to seven subjects the night before the recording. We noted that in most subjects there was a reduction in the spectral intensity of the alpha rhythm, associated with a greater frequency instability, several hours after the absorption of nitrazepam. This corresponds to the tardive hypnotic action of the psychotrope, the importance of which is wellknown at the present time. In the same way as the increase in rapid rhythms, the slipping of 0.5 c/s of the dominant alpha frequency to the top could be characteristic of the action of nitrazepam.

Adult↗

PubMed2001

Spatial-temporal structures of human alpha rhythms: theory, microcurrent sources, multiscale measurements, and global binding of local networks.

A theoretical framework supporting experimental measures of dynamic properties of human EEG is proposed with emphasis on distinct alpha rhythms. Robust relationships between measured dynamics and cognitive or behavioral conditions are reviewed, and proposed physiological bases for EEG at cellular levels are considered. Classical EEG data are interpreted in the context of a conceptual framework that distinguishes between locally and globally dominated dynamic processes, as estimated with coherence or other measures of phase synchronization. Macroscopic (scalp) potentials generated by cortical current sources are described at three spatial scales, taking advantage of the columnar structure of neocortex. New EEG data demonstrate that both globally coherent and locally dominated behavior can occur within the alpha band, depending on narrow band frequency, spatial measurement scale, and brain state. Quasi-stable alpha phase structures consistent with global standing waves are observed. At the same time, alpha and theta phase locking between cortical regions during mental calculations is demonstrated, consistent with neural network formation. The brain-binding problem is considered in the context of EEG dynamic behavior that generally exhibits both of these local and global aspects. But specific experimental designs and data analysis methods may severely bias physiological interpretations in either local or global directions.

Alpha Rhythm↗

PubMed1989

Dominant occipital (alpha) rhythm frequency in early stage Alzheimer's disease and depression.

The sinusoidal 8-13 Hz wave form that dominates in the occipital EEG record during relaxed wakefulness is known as alpha rhythm or dominant occipital rhythm. The frequency of this rhythm is known to decrease with normal aging with organic brain diseases. Here we report dominant occipital frequency (DOF) data for 41 early stage AD patients, 50 age-, sex- and health-matched control subjects and 22 subjects with major depressive disorder. DOF was assessed blindly for each subject from 10 or more samples during relaxed wakefulness in an all-night polysomnogram. Mean DOF was significantly lower in the AD (mean +/- S.D. was 8.24 +/- 1.04) than control group (9.48 +/- 0.57; F = 56, P less than 0.001). Mean DOF was also significantly lower in the depressed than control group (9.20 +/- 0.50 vs. 9.48, F = 5.0, P less than 0.05). In discriminant analyses, DOF achieved an overall correct classification rate of 77% for AD vs. control subjects, and 72% for AD vs. depressed subjects. These results indicate that DOF may be useful in identifying early stages of AD in healthy, drug-free populations.

Aged↗

PubMed2005

Correlating the alpha rhythm to BOLD using simultaneous EEG/fMRI: inter-subject variability.

Simultaneous recording of electroencephalogram/functional magnetic resonance images (EEG/fMRI) was applied to identify blood oxygenation level-dependent (BOLD) changes associated with spontaneous variations of the alpha rhythm, which is considered the hallmark of the brain resting state. The analysis was focused on inter-subject variability associated with the resting state. Data from 7 normal subjects are presented. Confirming earlier findings, three subjects showed a negative correlation between the BOLD signal and the average power time series within the alpha band (8--12 Hz) in extensive areas of the occipital, parietal and frontal lobes. In small thalamic areas, the BOLD signal was positively correlated with the alpha power. For subjects 3 and 4, who displayed two different states during the data acquisition time, it was shown that the corresponding correlation patterns were different, thus demonstrating the state dependency of the results. In subject 5, the changes in BOLD were observed mainly in the frontal and temporal lobes. Subject 6 only showed positive correlations, thus contradicting the negative BOLD alpha power cortical correlations that were found in most subjects. Results suggest that the resting state varies over subjects and, sometimes, even within one subject. As the resting state plays an important role in many fMRI experiments, the inter-subject variability of this state should be addressed when comparing fMRI results from different subjects.

Adult↗

PubMed1992

Alpha rhythm power and the effect of photic stimulation in migraine with brain mapping.

The topographic maps of 50 patients suffering from migraine with or without aura were compared to the brain maps of 20 normal controls and 20 patients with tension-type headaches. Only the migraine group showed a significant decrement of alpha rhythm power, during rest with eyes closed, at the posterior areas of the brain, and a significant increment of alpha power at the same regions during IPS at 20 c/sec.

Adolescent↗

PubMed1980

A neural net model for the alpha-rhythm.

Because of the enormous complexity which characterizes the activity of the brain a special effort has been made toward the development of neural models. These models are necessarily based on fundamental simplification of neural structures, and neural mechanisms. It is however necessary that any assumed mechanism be based on acceptable physiological criteria. We have developed such a model in the past (Anninos, 1969; Anninos et al., 1970) and in this paper we elaborate on it and attempt to incorporate in it a mechanism which will give rise to alpha-rhythm activity.

Alpha Rhythm↗

PubMedDate not supplied

[The spectral correlations of human brain electrical activity (the EEG) in the alpha-rhythm range occurring while performing latent inhibition].

Changes in perception of a stimulus and impairment of retrieval of memory trace resulted from the stimulus loss of novelty are called the latent inhibition (LI). The present study was undertaken to investigate the human LI using the analysis of changes in frequency power and coherence of the alpha rhythm. The results indicate that the loss of novelty of a stimulus is accompanied by a significant increase in the power of the upper alpha in the frontal regions of the right hemisphere and temporal regions of both hemispheres resulting in an impairment of memory retrieval in the frontal regions. Analysis of coherence changes revealed the reduction of interaction between the right temporal region and anteriofrontal, temporo-occipital, and right parietooccipital regions in response to administration of the conditioned words in comparison with the control ones. The findings suggest that the LI is a manifestation of the more general physiological process--the hidden inhibition.

Adolescent↗

PubMed2005

Pre- and poststimulus alpha rhythms are related to conscious visual perception: a high-resolution EEG study.

Conscious and unconscious visuospatial processes have been related to parietooccipital cortical activation as revealed by late visual-evoked potentials. Here the working hypothesis was that a specific pattern of pre- and poststimulus theta (about 4-6 Hz) and alpha (about 6-12 Hz) rhythms is differently represented during conscious compared with unconscious visuospatial processes. Electroencephalographic (EEG) data (128 channels) were recorded in normal adults during a visuospatial task. A cue stimulus appeared at the right or left (equal probability) monitor side for a "threshold time" inducing about 50% of correct recognitions. It was followed (2 s) by visual go stimuli at spatially congruent or incongruent position with reference to the cue location. Left (right) mouse button was clicked if the go stimulus appeared at the left (right) monitor side. Then, subjects said "seen" if they had detected the cue stimulus or "not seen" if missed (self-report). Sources of theta and alpha rhythms during seen and not seen EEG epochs were estimated by low-resolution electromagnetic brain topography software. Results showed that the prestimulus "low-band" (about 6-10 Hz) alpha rhythms in frontal, parietal, and occipital areas were stronger in power in the seen than in the not seen trials. After the visual stimulation, the power of the "high-band" (about 10-12 Hz) alpha rhythms in parietal and occipital areas decreased more in the seen than in the not seen trials. The present results suggest that visuospatial consciousness covary--presumably with a facilitatory effect--with the power of both pre- and poststimulus alpha rhythms.

Adult↗

PubMed1990

Spectral analysis of the EEG (alpha rhythm) and activity in the left hemisphere: the effects of lateral gaze.

This study tests the effect of maintaining right and left lateral gaze during a writing task which preferentially implicates the left hemisphere using an asymmetry parameter calculated from the spectral power of the alpha rhythm (RP-LP/RP + LP) in a right-handed patient undergoing the same experimental regimen nine times. A six derivation EEG was recorded. Maintaining left lateral gaze (toward the active hemisphere) removes the lateralization found during writing while staring straight ahead whereas maintaining right lateral gaze (toward the side opposite the active hemisphere) results in slightly lower values which are however, not significantly different from those obtained during staring straight ahead. This study adds an electrophysiologic aspect to Kinsbournes's paradigm on gaze position and hemispheric activation.

Adult↗

PubMed2001

Eeg alpha rhythm and glucose metabolic rate in the thalamus in schizophrenia.

Positron emission tomography with uptake of [(18)F]fluorodeoxyglucose (FDG) and quantitative EEG were simultaneously performed in 18 medication-free patients with schizophrenia and in 13 normal volunteers. Subjects performed the Continuous Performance Task (CPT) during FDG uptake. Correlations were calculated between alpha power during the CPT and glucose metabolic rate (GMR) in thalamic regions and between alpha power during the CPT and GMR in occipital cortices. Regression analyses were used to describe the prediction of GMR in the occipital cortices and in the thalamic regions of occipital alpha power. In normal controls, we found (1) significant negative correlations between absolute alpha power and GMR in the left occipital cortex, (2) significant positive correlations between normalized alpha power and GMR in the right and left lateral thalamus and (3) combined effects of GMR in the thalamic regions and the occipital cortices on alpha power, which accounted for 98% of the variance of alpha power. In patients with schizophrenia, we found no significant correlations between alpha power and GMR in the occipital cortices or between alpha power and GMR in the thalamic regions. Correlation coefficients between absolute alpha power and GMR in the left occipital cortex and between normalized alpha power and GMR in the left lateral thalamus were significantly different in normal subjects compared to schizophrenic patients. The present findings provide evidence for involvement of the thalamus in the generation of alpha rhythm in humans. Furthermore, the present results suggest differences in thalamocortical circuits between normal controls and schizophrenic subjects.

Adult↗

PubMed1981

[Effect of hyperventilation on depression of the EEG alpha rhythm caused by a suggested visual image].

An induction of an imagined visual sensation with the eyes closed can be regarded as a form of self-suggestion in the state of wakefulness. On receiving an instruction on imagining a visual sensation most healthy persons show a sharp weakening of disappearance of the alpha-rhythm depression on the EEG (in distinction from subjects who have not had hyperventilation). These findings point to an importance of using electroencephalography in combination with hyperventilation in psychotherapeutic practice for objective estimation of the effect of suggestion in wakefulness.

Adolescent↗

PubMed1981

Cortical alpha rhythm, biofeedback, and the determinants of subjective state.

A critical assumption in the rationale for the clinical application of voluntary control over central nervous system (CNS) activity is that there exists a direct relationship between specific CNS activities and specific subjective mood states. The experiment reported here was based on the idea that a joint manipulation of both cognitive and physiological (i.e., alpha electroencephalographic [EEG]) variables would provide information required for an explication of the processes involved in subjective mood change. Three main variables were considered in the present experiment. First, the instructions were designed to induce a "set" or expectations for either positive or negative changes in subjective mood. Second, the type of feedback (alpha or not alpha) was varied. Those in the not-alpha feedback condition received feedback contingent on the absence of alpha activity, whereas those in the alpha feedback condition received feedback contingent on the presence of alpha activity. Third, an estimate of each individual's baseline alpha density was obtained, and on this basis subjects were classified as high-baseline or low-baseline subjects. Baseline alpha density, alpha density during training, and subjective mood were all considered as continuous variables. The results of the present study indicate that biofeedback of the cortical alpha rhythm is neither a sufficient nor a necessary condition for changes in subjective mood. In addition, the type of instructions designed to set subjects for positive or negative alterations in subjective states is predictive of changes in subjective state reported during alpha biofeedback training as well as of success at controlling and changing EEG during feedback training. The data presented here permit a direct examination of the actual relationship of EEG changes to changes in subjective mood state. Similar shifts in subjective mood state can be obtained with either increases or decreases in alpha activity. Further, both positive and negative subjective experiences can be associated with increases in alpha activity.

Adult↗

PubMed1952