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PubMed1984

The functional significance of event-related desynchronization of alpha rhythm in attentional and activating tasks.

The functional significance of event-related desynchronization (ERD) of alpha rhythm was investigated in a task which manipulated cognitive load and event rate. It was found that with increasing cognitive load the amount and duration of ERD increased. When a slow event rate was used the mean relative desynchronization of alpha rhythm and duration of ERD increased. These effects were found to be independent of one another. These results were interpreted as indicating that the mean ERD of alpha rhythm is sensitive to the selective attention demands of a task and the surprise value of stimuli.

Adult↗
PubMed1974

Phase relationships of alpha rhythm in man.

Stationary phase relationships of human scalp EEGs in the frequency range of the alpha rhythm were examined by the method of cross-spectral analysis. EEGs were recorded from midsaggital points equally spaced on the scalp in normal and blind adults. Cross-spectral analysis was applied to one- or three-minute records and to successive q0-second records. The generalized component, which usually formed a dominant peak in the EEG spectra, showed a gradual phase advance toward the frontal region but seldom reached 180 degrees, and the phase shift at intermediate points was not linearly related to the distance between them. A parallel relation was confirmed between the increase in the inter-regional phase difference and the decrease in the coherence value. A variety of phase differences was noticed for the more localized subordinate component, and the angles of this component ranged more broadly than with the generalized dominant component. Phase relations of the alpha rhythm in the blind were similar to those of the localized component in normal subjects. Thus, in respect to inter-regional relationships in the antero-posterior direction, the alpha rhythms were classified into at least two types, one closely related to the visual function and the other depending upon some functions other than visual. Effectiveness of the cross-spectral analysis on phase relations of the EEG was discussed in comparison with other methods.

Adolescent↗
PubMedDate not supplied

[A model of the structure of the dipole source of the alpha rhythm in the human visual cortex].

The model of the alpha-rhythm was studied which consisted of a set of elementary dipoles. The dipoles were fixed normally to the surfaces of a cruciform structure which imitated the structure of the visual cortex. The magnitude of dipole moments varied according to the sinusoidal low. Thus, the effect was produced of the waves leaving the epicenters which in one case were located in the lower parts of the cruciform structure and at the ends of the side rays of this structure in the other case. The model enabled imitation of all experimentally found phenomena of the alpha-wave travelling (fronto-occipital travelling, rotatory travelling, diagonal and transverse forms). Additionally, the phenomenon was found which enabled simulation of the flat EEG with remaining cortical alpha activity. The possible velocity of the alpha-wave propagation in the visual cortex was calculated. The model can be applied for testing the hypothesis that the alpha-rhythm is a scanning mechanism in the visual cortex.

Alpha Rhythm↗
PubMed2001

Computational model of thalamo-cortical networks: dynamical control of alpha rhythms in relation to focal attention.

EEG/MEG rhythmic activities such as alpha rhythms, of the visual or of the somato-sensory cortex, are commonly modulated as subjects perform certain tasks or react to specific stimuli. In general, these activities change depending on extrinsic or intrinsic events. A decrease of the amplitude of alpha rhythmic activity occurring after a given event, which manifests as a decrease of a spectral peak, is called event-related desynchronization (ERD), whereas the inverse is called event-related synchronization (ERS), since it is assumed that the power of a spectral peak is related to the degree of synchrony of the underlying oscillating neuronal populations. An intriguing observation in this respect [Pfurtscheller and Neuper, Neurosci. Lett. 174 (1994) 93-96] was that ERD of alpha rhythms recorded over the central areas was accompanied by ERS, within the same frequency band, recorded over neighboring areas. In case the event was a hand movement, ERD was recorded over the scalp overlying the hand cortical area, whereas ERS was concomitantly recorded over the midline, whereas if the movement was of the foot the opposite was found. We called this phenomenon 'focal ERD/surround ERS'. The question of how this phenomenon may be generated was approached by means of a computational model of thalamo-cortical networks, that incorporates basic properties of neurons and synaptic interactions. These simulation studies revealed that this antagonistic ERD/ERS phenomenon depends on the functional interaction between the populations of thalamo-cortical cells (TCR) and reticular nucleus cells (RE) and on how this interaction is modulated by cholinergic inputs. An essential feature of this interaction is the existence of cross-talk between different sectors of RE that correspond to distinct sensory modules (e.g. hand, foot). These observations led us to formulate the hypothesis that this basic neurophysiological mechanism can account for the general observation that enhanced attention given to a certain stimulus (the focus) is coupled to inhibition of attention to other stimuli (the surround).

Alpha Rhythm↗
PubMed1996

Intention as a component of the alpha-rhythm response to mental activity.

Many studies of alpha-rhythm reactivity conclude that alpha is selectively attenuated by attention accompanying mental activity. The topography of this attenuation is assumed to match the relevant functional topography of the cortex. But there are reports of apparent increased attention resulting in no change, or even enhanced alpha - the paradoxical response. It is proposed that in this case, alpha amplitude may be dependent on an intention component of behaviour. Some conflicting reports of alpha reactivity to mental processes may then be resolved. It is argued that the classical attention model of alpha is untenable, except for simple sensori-motor responses. Reasons are given to support this and the concept of intention as a neuropsychological variable is introduced. Evidence is presented for a generalisation of an oculomotor model of alpha activity proposed by Wertheim who demonstrated that alpha reduces during attentive, but not during intentive visual behaviour. The generalisation follows from reports of enhanced alpha in the few seconds prior to a skilled action in sport, and by neurophysiological evidence for a separate cortical organisation for perception and action. Varying proportions of attention and intention then add a dimension to the factors influencing alpha blocking which may explain its inconsistent response.

Adult↗
PubMed2002

[Rhythmic photostimulation and a number of alpha-rhythm dipoles in the human brain].

Dynamic study of the equivalent current dipoles (ECDs) of alpha rhythm in the human brain was performed in a one-dipole model. The number of ECDs was shown to be dependent on the time course of visual stimulation, on the phase shift of triggering of flickers with alpha-rhythm frequency from alpha-wave, as well as on the type of visual illusions produced in subjects by this stimulation. The data are discussed in accordance with the "scanning hypothesis" that predict a certain functional meaning of the spreading alpha-wave for cortical processing of sensory information in the human brain.

Adolescent↗
PubMedDate not supplied

[The spatial and temporal variability of the magnetoencephalogram alpha rhythm in the normal human subject].

Using one-channel SQUID biomagnetometer alpha rhythm was recorded in five healthy men and eight healthy women. Maps of distribution of maximum values of mean MEG amplitudes were analyzed. Most frequently MEG maxima predominated in the parietal parts of the head. Less frequently they were found in the occipital parts. In single instances they could be found in the posterocentral sections and on the midline. In most cases an amplitude interhemispheric asymmetry of extrema was revealed. In men the mean amplitude of the alpha-rhythm predominated more frequently on the left side and in women--on the right one. The map of distribution of mean amplitudes was stable at least during two weeks. Narrow-band filtration allowed to reveal up to three discrete amplitude modes. At definite frequencies the MEG amplitude was continuously stable during several seconds.

Adult↗
PubMed1980

Normative spectral data on alpha rhythm in male adults.

Spectral analysis of the EEGS of 110 normal male subjects was carried out in order to obtain objective normative data on the alpha rhythm. The parameters of alpha rhythm extractd from the spectra and coherency functions were: the frequency and bandwidth, maximum power density, interhemispheric symmetry, reactivity, coherency and their interrelationships.

Adolescent↗
PubMed1991

Influence of lateralized neuropsychological activities with and without sensorimotor components on EEG spectral power (alpha-rhythm).

Spectral analysis of the EEG (alpha-rhythm) was studied in 8 young right-handed men who underwent 6 experimental tasks which were compared with rest, and included two pure motor activities using only the right and then the left hand, two pure neuropsychological tasks, and two "mixed" tasks with both neurophysiological and motor activities. The electrophysiological parameters studied were the log of spectral power and an asymmetry index (RP-LP)/(RP + LP). In order to demonstrate lateralization of the EEG, one must associate lateralized motor and neuropsychological tasks (which are supposed to preferentially involve one of the cerebral hemispheres). These results may reconcile apparently divergent views published in the literature with respect to lateralized EEG modifications associated with cognitive activities.

Adult↗
PubMed2006

Scaling and organization of electroencephalographic background activity and alpha rhythm in healthy young adults.

The coexistence of the broad-band fluctuation and alpha rhythm of the brain dynamics is studied based on the zero-crossing property of the local electroencephalographic (EEG) recording in eyes closed and eyes open. A two-component zero-crossing scenario, consisting of a broad-band fractal and narrow-band rhythm components, is assumed. Scaling is found in the power law distribution p(tau) approximately tau(-nu) of the crossing time interval tau of the broad-band fluctuation. In alpha dominant brain state, the alpha rhythm interval L also exhibits scaling in the form of power law distribution: p(L) approximately L(phi). Our main result is the relationship nu + phi approximately 3 that characterizes the organization of these two prominent features of the brain dynamics. The possible role of self-organized criticality of punctuated equilibrium in this organization is discussed.

Adult↗
PubMed1998

Neural networks for generation and suppression of alpha rhythm: a PET study.

To study neuronal activities that influence the generation of the alpha rhythm, we used positron emission tomography and simultaneous recording of the electroencephalogram (EEG) in normal volunteers and under passive conditions. A negative correlation between regional cerebral blood flow and alpha power was found in the occipital cortex, consistent with the visual modality-specific reactivity of the alpha rhythm. A positive correlation was found in the pons, midbrain, hypothalamus, amygdala, the basal prefrontal cortex, insula and the right dorsal premotor cortex. Neuronal activities of the brain stem and limbic system that are positively correlated with alpha power may provide an anatomical basis for studies of the relationship between emotional state and brain rhythm in health and disease.

Adult↗
PubMed1990

Alpha rhythm in classical migraine (migraine with aura): abnormalities in the headache-free interval.

The alpha rhythm of 18 patients with classical migraine (migraine with aura) was studied by EEG spectrum analysis for evidence of neural abnormalities during the asymptomatic period. The temporal relationship of the findings to attacks was studied by serial records in 11 cases. Increased frequency dispersion and frequency asymmetries of the alpha rhythm were found. The records were, however, mostly normal when separated from attacks by at least 10 asymptomatic days. The abnormalities increased significantly before the onset of prodromal symptoms and clearly outlasted the headache phase. The results give evidence of a fluctuating asymmetric neural disorder in classical migraine.

Adult↗
PubMed2005

Evaluating the entrainment of the alpha rhythm during stroboscopic flash stimulation by means of coherence analysis.

Two major conflicting hypotheses propose that alpha rhythm activity should be either the output of a linear filter having a white noise as input or reflect the output of a nonlinear oscillator. External stimulation can be employed to test for nonlinearity in alpha genesis, since an entrainment of such rhythmic activity (shift in the alpha peak) could only be explained by nonlinear relationships. Flash photic stimulation has been used to investigate such entrainment. Nevertheless, only entrainments due to the second harmonic of the stimulation could be suitably measured. Aiming at overcoming this limitation, a coherence-based technique is proposed for evaluating the strength of responses due to rhythmic stimulation. It was applied to the occipital EEG derivations of 12 normal subjects during stroboscopic stimulation. Entrainment of alpha rhythm by the second harmonic of the stimulation occurred in 75% of the subjects, whilst no spectral shifts were observed for the remained that exhibited broadband alpha peak at rest. However, stimulating with fundamental frequency close to that peak led to entrainment in all subjects. These differences in the degree of synchronization due to stimulation at the first and second harmonics should reflect complex nonlinear mechanisms in alpha genesis.

Adolescent↗
PubMed1978

Thalamic control of spontaneous alpha-rhythm and evoked responses.

EEG, depth recordings from the thalamus, visual-evoked potentials, and readiness motor potentials were analyzed with a computer in 40 patients with involuntary movements and intractable pain who underwent stereotactic thalamotomy. It was demonstrated that there were significant correlations in alpha-rhythms between the ventrolateral (VL) nucleus and the frontocentral cortex, and also between the centromedian nucleus and the centroparietal cortex, with the phase difference of the cortex lagging behind the thalamus. Relationships between the thalamic VL nucleus and the frontocentral cortex were significant not only in alpha-rhythms, but also in evoked responses following photic stimulations, voluntary movements, and electrical thalamic stimulation. Thalamotomy produced a bilaterally decreased synchronization of the cortical alpha-rhythms, which recovered within 6 months.

Alpha Rhythm↗
PubMedDate not supplied

[Functional brain asymmetry and alpha rhythm amplitude].

The dynamics of the EEG alpha-rhythm asymmetry was studied in 42 subjects before and in the process of verbal activity. Three groups of subjects were identified. 1. The first group was characterized by the dominant activation of the left hemisphere in the background activity and during the first presentations of functional loads. With subsequent presentations the right hemisphere became more activated. 2. In subjects of the second group the right hemisphere was initially more activated. The left hemisphere was more activated only during the first presentations of functional loads. At the final stages, their right hemisphere became again more activated. 3. The third group of subjects was identified by the high level of activation of the right hemisphere in the background activity and during the first presentations of functional loads, and by activation of the right hemisphere at the final stages.

Acoustic Stimulation↗
PubMed1999

Spatial structure of the human alpha rhythm: global correlation in adults and local correlation in children.

OBJECTIVE: The maturation of the neocortex during childhood and adolescence involves dramatic increases in white-matter volume. EEG recordings from children and adults were examined to determine whether there are associated changes in spatial properties of dynamic processes in the neocortex. METHODS: Spontaneous eyes-closed and eyes-open EEG were recorded at 128 electrodes in 20 children aged 6-11 years and 23 adults aged 18-23 years. The surface Laplacian algorithm was applied to improve the spatial resolution of each electrode. Power and coherence were used to characterize the spatial structure of the alpha rhythm. A stochastic field model was used to eliminate coherences that are inflated due to volume conduction. RESULTS: In adults, the alpha rhythm is characterized by very high coherence between distant electrodes. The children demonstrated reduced anterior power and coherence between anterior and posterior electrodes at the peak alpha frequency in comparison to the adults. The Laplacian alpha rhythm demonstrated much higher power in the children at both anterior and posterior electrodes, but was weakly correlated between electrodes. CONCLUSIONS: The maturation of neocortex in late childhood involves increased global correlation by long-range corticocortical connections. The local correlation that contributes power to each electrode, independent of other electrodes, is reduced as the global correlation increases.

Adolescent↗
PubMed2006

Distraction affects frontal alpha rhythms related to expectancy of pain: an EEG study.

Previous electroencephalographic (EEG) evidence has shown event-related desynchronization (ERD) of alpha rhythms before predictable painful stimuli, as a possible neural concomitant of attentional preparatory processes (Babiloni, C., Brancucci, A., Babiloni, F., Capotosto, P., Carducci, F., Cincotti, F., Arendt-Nielsen, L., Chen, A.C., Rossini, P.M., 2003. Anticipatory cortical responses during the expectancy of a predictable painful stimulation. A high-resolution electroencephalography study. Eur. J. Neurosci. 18 (6) 1692-700). This study tested the hypothesis that alpha ERD before predictable painful stimuli is reduced as an effect of distraction. A visual warning stimulus preceded a laser painful stimulation, which was strictly followed by visual imperative stimuli. In the Pain (control) condition, no task was required after the imperative stimuli. In the Pain + Movement condition, subjects had to perform a movement of the right index finger. In the Pain + Cognition condition, they had to mentally perform an arithmetical task. EEG data were recorded in 10 subjects from 30 electrodes. Artifact-free recordings were spatially enhanced by surface Laplacian transformation. Alpha ERD was computed at three alpha sub-bands according to subjects' individual alpha frequency peak (i.e., about 6-8 Hz, 8-10 Hz, 10-12 Hz). Compared to the control condition, the subjects reported a significantly lower stimulus intensity perception and unpleasantness in the Pain + Movement and Pain + Cognition conditions. In addition, there was a cancellation of the alpha 3 ERD (i.e., about 10-12 Hz) in Pain + Cognition condition and even a generation of a statistically significant alpha 3 ERS in Pain + Movement condition. These effects were maximum over fronto-central midline. These results suggest that distraction during the expectancy of pain is related to a reduced neural desynchronization of fronto-central midline alpha rhythms (i.e., reduced cortical activation) towards an overt hyper-synchronization (cortical idling).

Adult↗