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PubMed1999

EEG alpha rhythm in infants.

The 'functional topography' approach has been applied to study alpha rhythms in infant twins during the second half-year of life. The experimental sample included 154 normal infants born at 32-41 weeks of gestational age. Their chronological age varied from 7.4 to 12.4 months. EEG was registered during wakefulness under two experimental conditions: sustained visual attention and dark homogenous visual field. During darkness as compared with visual attention the sharp increase of spectral amplitudes within 5.2-9.6 Hz band was observed over the occipital-parietal cortex. The properties of the 5.2-9.6 Hz occipital rhythmic activity comply with the classical properties of alpha rhythm. The distinct spectral peak in 6.0-8.8 Hz band at precentral recording sites was observed during sustained visual attention. This rhythmic component was suppressed under the condition of total darkness. Arguments in favour of homology between the infant central rhythm and adult sensorimotor mu rhythm are advanced. The group mean of alpha peak frequency increased from 6.24 +/- 0.45 Hz at 8 months to 6.78 +/- 0.38 Hz at 11 months of chronological age. The frequency of infant alpha rhythm depended only on the period of extrauterine experience, regardless of gestational age at birth. This result points to the critical role of early visual experience in alpha rhythm development. The group mean of the peak frequency of mu rhythm also increased during the second half-year of life, from 7.03 +/- 0.47 Hz at 8 months to 7.42 +/- 0.46 Hz at 11 months. Unlike alpha rhythm, the peak frequency of mu rhythm depended on duration of both intra- and extrauterine development. We speculate that the development of sensorimotor mu rhythm is influenced by somatosensory stimulation, which, in sharp contrast to the visual input, is present in the uterus.

Age Distribution↗
PubMed1999

Dynamics of the human alpha rhythm: evidence for non-linearity?

OBJECT: For a better understanding of the physiological mechanisms responsible for alpha rhythms it is important to know whether non-linear processes play a role in their generation. We used non-linear forecasting in combination with surrogate data testing to investigate the prevalence and nature of alpha rhythm non-linearity, based on EEG recordings from humans. We interpreted these findings using computer simulations of the alpha rhythm model of Lopes da Silva et al. (1974). METHODS: EEGs were recorded at 02 and O1 in 60 healthy subjects (30 males; 30 females; age: 49.28 years; range 11-84) during a resting eyes-closed state. Four artefact-free epochs (2.5 s; sample frequency 200 Hz) from each subject were tested for non-linearity using a non-linear prediction statistic and phase-randomized surrogate data. A similar type of analysis was done on the output of the alpha model for different values of input. RESULTS: In the 480 (60 subjects, 2 derivations, 4 blocks) epochs studied, the null hypothesis that the alpha rhythms can result from linearly filtered noise, could be rejected in 6 cases (1.25%). The alpha model showed a bifurcation from a point attractor to a limit cycle at an input pulse density of 615 pps. Non-linearity could only be detected in the model output close to and beyond this bifurcation point. The sources of the non-linearity are the sigmoidal relationships between average membrane potential and output pulse density of the various cells of the neuronal populations. CONCLUSION: The alpha rhythm is a heterogeneous entity dynamically: 98.75% of the epochs (type I alpha) cannot be distinguished from filtered noise. Apparently, during these epochs the activity of the brain has such a high complexity that it cannot be distinguished from a random process. In 1.25% of the epochs (type II alpha) non-linearity was found which may be explained by dynamics in the vicinity of a bifurcation to a limit cycle. There is thus experimental evidence from the point of view of dynamics for the existence of the two types of alpha rhythm and the bifurcation predicted by the model.

Adolescent↗
PubMed1979

Personality and male-female influences on the EEG alpha rhythm.

The amplitude and frequency of the alpha rhythm was measured in electroencephalic recordings from 45 male and 46 female university students. The mean alpha frequency of the female group was significantly greater than the male group. There was no significant difference in alpha frequency between females in the first half of the menstrual cycle and those in the second half. The relationship between questionnaire measures of psychoticism, extraversion and neuroticism, and the alpha rhythm was investigated using analysis of variance, correlation analysis and factor analysis. Alpha amplitude was significantly greater in extraverted subjects, alpha amplitude and extraversion scores were significantly correlated and both had high loadings on a single factor. No relationship between psychoticism or neuroticism and alpha frequency or amplitude was observed.

Adult↗
PubMed1979

[Adaptive regulation of cerebral biopotentials (alpha-rhythm) in neurotic patients].

With the aid of a feedback towards an increase in the EEG intensity, adaptive regulation of brain biopotentials (alpha-rhythm) was conducted in 22 patients with different forms of neurosis. It was established that in patients with an initial low level of alpha-rhythm its regulation was more significant, while in patients with an initially middle level of alpha-rhythms in the EEG, its regulation was less expressed. The clinical effect of regulation in all cases was positive. The study also demonstrated a crosscorrelation of connections in the process of regulation between such functions as alpha-rhythm-EMG, alpha-rhythm-SGR, etc. It is suggested that, regulation of alpha-rhythms can be accepted as a therapeutic approach in the treatment of patients with neuroses.

Adult↗
PubMedDate not supplied

[The spatial structure of the alpha rhythm in the healthy human being studied by EEG mapping].

EEG study was conducted in the state of relative rest in 15 healthy subjects with predominance of the alpha rhythm. Data processing was performed on neuromapper ("Neuroscience", Great Britain). Principal attention was paid to the dynamics of spatial-temporal relations of the alpha rhythm. Cyclic changes were shown of the alpha-rhythm amplitude, proceeding with change of high and low amplitudes during seconds, varying in time in various individuals. Three types of spatial distribution of the alpha rhythm over the cortex at the relative rest were obtained: 1) generalized distribution over the cortex with the wavy shift of the frequency fields; 2) formation of delimited local zones of the alpha rhythm, differing by the frequency from the rhythm in other cortical areas; 3) local zone of the low-frequency alpha rhythm in the visual projection zone (18 and 19 fields). Change of the distribution types of the alpha rhythm in the state of rest takes place in the seconds of time intervals, corresponding, according to the literature data, to the proceeding of elementary mental processes.

Adult↗
PubMed1980

Relative contributions of intracortical and thalamo-cortical processes in the generation of alpha rhythms, revealed by partial coherence analysis.

The thalamo-cortical relationships of alpha rhythms have been analysed in dogs using partial coherence function analysis. The objective was to clarify how far the large intracortical coherence commonly recorded between different cortical sites could depend on a common thalamic site. It was found that the alpha rhythms of the LGN influenced only moderately the coherence between cortical alpha rhythms whereas that of the pulvinar had much more influence, at least in relation to some cortical areas. Significant phase shifts between thalamus and cortex were also measured. The results demonstrate that there are thalamo-cortical and cortico-cortical components which interact in the generation of cortical alpha rhythms.

Alpha Rhythm↗
PubMed1990

[Reappearance and recovery of alpha rhythm after eye opening].

To obtain more informations from routine EEG recording, we studied changes in alpha rhythm after eye opening that had been almost disregarded hitherto. The study was carried out on 26 normal controls and 137 patients with four categories of diseases including 52 patients with psychiatric diseases, 8 with trifling neurological symptoms, 68 with defined organic brain diseases, and 9 with headache without defined organic cause. Following routine EEG recording, each subject was asked to keep their eyes opened for three minutes. The major changes in alpha rhythm after eye opening were composed of two patterns; "reappearance" and "recovery". The reappearance was defined as appearance of 5 or more alpha waves in series; and the recovery, as the amount and amplitude of the alpha rhythm became equal to those of the back ground alpha-rhythm which was seen while their eyes were kept closed. The reappearance was noticed in 84.6% of normal controls and in 89.1% of all patients. In patients with organic brain diseases, the reappearance was seen in 88.2%, while it was in 68.6% of the patients without organic brain disease. The recovery was noticed in 34.3% of all patients (p less than 0.01), while it was only in 15.4% of normal controls. The incidence of the recovery in the patients with organic brain diseases was 41.2%, the value of which was significantly higher than that of the rest of patients (28.8%, 15 out of 52 patients, p less than 0.05). These patients with the recovery tended to show slower frequency and higher amplitude in the back ground alpha-rhythm than the patients without recovery.

Adolescent↗
PubMed1985

[Extraordinary variant of the alpha rhythm].

The authors describe a variant of alpha rhythm, which is remarkable because of its great amplitude (200-300 microV). It is observed quite exceptionally in children and adolescents with a severe encephalopathy of either ante- or perinatal etiology. They suggest that the surplus amplitude of this alpha rhythm could depend upon a deafferentation of the occipital cortex in patients with severe amblyopia.

Agenesis of Corpus Callosum↗
PubMed2004

Sub-second "temporal attention" modulates alpha rhythms. A high-resolution EEG study.

In the present high-resolution electroencephalographic (EEG) study, event-related desynchronization/synchronization (ERD/ERS) of alpha rhythms was computed during an S1-S2 paradigm, in which a visual cue (S1) predicted a SHORT (600 ms) or LONG (1400 ms) foreperiod, preceding a visual go stimulus (S2) triggering right or left finger movement. Could orienting attention to a selective point in time influence the alpha rhythms as a function of the SHORT vs. LONG foreperiod? Stronger selective attentional modulations were predicted for the SHORT than LONG condition. EEG data from 54 channels were "depurated" from phase-locked visual evoked potentials and spatially enhanced by surface Laplacian estimation (i.e., final data analysis was conducted on 16 subjects having a sufficient number of artifact-free EEG single trials). Low-band alpha rhythms (about 6-10 Hz) were supposed to be related to anticipatory attentional processes, whereas high-band alpha rhythms (10-12 Hz) would indicate task-specific visuo-motor processes. Compared to the LONG condition (foreperiod), the SHORT condition induced a quicker and stronger ERS at low-band alpha rhythm (about 6-8 Hz) over midline and bilateral prefrontal, sensorimotor, and posterior parietal areas. In contrast, the concomitant high-band alpha (about 10-12 Hz) ERD/ERS showed no significant difference between the two conditions. In conclusion, temporal attention for a sub-second delay (800 ms) did modulate low-band alpha rhythm over large regions of both cortical hemispheres.

Adolescent↗
PubMed2004

Propofol-induced alpha rhythm.

The electroencephalographic effects of two intravenous sedative/hypnotic drugs, propofol and thiopental, were studied at three stable blood concentrations in 52 normal healthy volunteers. The higher concentration resulted in unresponsiveness (lack of response to auditory/tactile stimuli) in all subjects. This report describes the strong frontal-central rhythms apparent in this state using a quantitative description of oscillatory systems underlying the rhythm. These rhythms occur when sedative drug concentrations are greater than those producing the well-described increase in broadband beta-power associated with many sedative drugs. Propofol induces rhythms in the alpha-range, while thiopental produces rhythms in the beta-range. Quasistationary for a period of about 1 h, these rhythms exceed the baseline alpha-rhythm in power. By their resonant nature, these propofol-induced rhythms are analogous to 'the classic alpha-rhythm', but quantitative characteristics of the underlying oscillatory systems are different. Baseline properties of the oscillatory system underlying the initial resting alpha-rhythm recover completely as drug concentration decays to negligible values.

Adult↗
PubMed1999

MEG characterization of spontaneous alpha rhythm in the human brain.

The present piece of research studied the spontaneous alpha rhythm of the human brain by combining the use of a whole-cortex neuromagnetometer and Magnetic Resonance Imaging. Single trials of spontaneous brain activity were recorded from ten human subjects asked to rest, with their eyes either closed or open, in relaxed wakefulness. MEG measurements were conducted over a period of one and a half years. The replicability of the results was confirmed for eight subjects out of ten. For three subjects, the alpha rhythm did not show any reductions due to the opening of the eyes. Both field map pattern and location of the estimated source were persistently stationary during each of the bursts of oscillations of the alpha rhythm. Dipoles were concentrated in clusters, indicating the existence of several spatially distributed sources. The calcarine fissure, the parieto-occipital sulcus and the surrounding occipital and parieto-occipital areas were identified as cortical sites of the brain where the alpha rhythm may originate. For four subjects, the majority of the sources were located near or in the calcarine fissure, while for five subjects, they were located near or in the parieto-occipital sulcus and for the remaining subject they were equally divided between the two generation sites.

Adult↗
PubMed2005

Thalamic mechanisms of EEG alpha rhythms and their pathological implications.

During relaxed wakefulness, the human brain exhibits pronounced rhythmic electrical activity in the alpha frequency band (8-13 Hz). This activity consists of 3 main components: the classic occipital alpha rhythm, the Rolandic mu rhythm, and the so-called third rhythm. In recent years, the long-held belief that alpha rhythms are strongly influenced by the thalamus has been confirmed in several animal models and, in humans, is well supported by numerous noninvasive imaging studies. Of specific importance is the emergence of 2 key cellular thalamic mechanisms, which come together to generate locally synchronized alpha activity. First, a novel form of rhythmic burst firing, termed high-threshold (HT) bursting, which occurs in a specialized subset of thalamocortical (TC) neurons, and second, the interconnection of this subset via gap junctions (GJs). Because repetitive HT bursting in TC neurons occurs in the range of 2 to 13 Hz, with the precise frequency increasing with increasing depolarization, the same cellular components that underlie thalamic alpha rhythms can also lead to theta (2-7 Hz) rhythms when the TC neuron population is less depolarized. As such, this scenario can explain both the deceleration of alpha rhythms that takes place during early sleep and the chronic slowing that characterizes a host of neurological and psychiatric disorders.

Alpha Rhythm↗
PubMed1999

Human brain alpha rhythm: nonlinear oscillation or filtered noise?

The mechanism for generation of the alpha rhythm is controversial. In the current study, analysis in the time and frequency domains revealed that the alpha rhythm recorded from the scalp overlying the human occipital cortex can be entrained to the second or third harmonic of low frequency light flashes. These results support the view that the alpha rhythm is generated by a nonlinear oscillator rather than a narrow-band transmission system acting as a filter.

Adult↗
PubMedDate not supplied

[Visual illusions and the alpha-rhythm EEG].

During flicker stimulation with the alpha-rhythm frequency through the closed eyes 11 from 12 subjects clearly saw illusory objects (in order of descending probability, ring, circle, three-dimensional spiral or spiral spring, funnel, curved crossed bars). The individual optimal stimulation frequency for producing an illusion was always within the alpha range and was closely correlated with the individual dominant alpha frequency (r = 0.86). A supposition is discussed that the effect obtained is based on the quasistroboscopic fixation of the spreading cortical excitation wave of the alpha-rhythm due to its summation with the isorhythmic afferent diffuse cortical excitation evoked by flashes. This phenomenon enables "freezing" of the alpha wave at a certain instant of its spreading and makes it "visible".

Adult↗
PubMed1989

[The lability of the human background alpha rhythm under functional loads].

Some characteristics of electroencephalographic reaction (alpha frequency, whole alpha range power spectrum and alpha index) have been studied. In the first series the indifferent single, rhythmic and complex stimuli were presented to the test subjects, in another series a conditioned motor reflex was elaborated, in the third series the test subjects rhythmically reproduced fixed temporal interval. It has been shown that the functional loads lead to higher alpha frequency. The alpha rhythm frequency was higher in subjects verbally underestimating and reproducing intervals with some delay than in ones overestimating intervals and reproducing them in advance. It has been suggested that alpha rhythm instability is due to reorganization processes in neuronal complexes of different lability.

Acoustic Stimulation↗
PubMed1997

Modulation of the parieto-occipital alpha rhythm during object detection.

Changes in the human neuromagnetic alpha rhythm were monitored during an object detection task to study the effects of visual shape processing on the parieto-occipital activity. Pictures of coherent meaningful objects, which the observers had to detect, and of disorganized meaningless non-objects were presented briefly between masks. The non-objects were systematically followed by a higher level of alpha than the objects, the difference emerging on average 400 msec after the stimulus, with a median delay of 130 msec after evoked response onsets in the occipital, temporal, and parietal cortices. Without attention to visual shape, the alpha levels did not differ between objects and non-objects. The alpha level was higher after non-objects than missed objects, and higher after missed than correctly detected objects, suggesting that the alpha level is inversely related to saliency or familiarity of the object and does not directly reflect visual awareness. The reactive alpha rhythm was generated in the parieto-occipital sulcus, which in several primate species includes areas belonging to the dorsal visual pathway. According to current views, the parietal cortex produces attentional signals that filter out irrelevant information in the ventral visual stream. Our results reinforce the idea of bidirectional interaction: information derived from visual shape can rapidly modify activity in the parieto-occipital region. The synchronized alpha oscillations may reflect attenuation of occipito-parietal information transfer and disengagement of parietal cortex from object selection.

Adult↗
PubMedDate not supplied

[The dynamic localization of a dipole source of the alpha rhythm in the human brain].

In 11 subjects the dynamic localization (with 2-ms step) of the equivalent current dipole of alpha rhythm during travelling alpha waves was studied using one-dipole 3-layered spherical head model and MRI. The dipole was localized in the occipital cortex and during the development of a single alpha wave it shifted in one or another direction while dipole's moment revealed fan-like rotation mainly in sagittal and horizontal planes. The results obtained indicate changing localization of the alpha-rhythm source in the region corresponding to striate cortex. They seem to prove scanning hypothesis that is still under discussion.

Adult↗