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PubMed1997

Alpha rhythm parameters and short-term memory span.

The study examined a statement from the neurophysiological model of A.N. Lebedev as to whether short-term memory span is related to a ratio of the alpha-rhythm frequency and parameters of step-type behaviour of wave processes in the EEG alpha range. Forty young healthy subjects performed a digit memory test. EEG signals were recorded from the occipital area during a resting period with eyes closed. As one of the parameters of step-type behaviour of alpha oscillations a mean value of the difference between periods of neighbouring peaks in the alpha spectra was calculated. A second parameter--the duration of alpha spindles, considered to be a superposition of alpha oscillations--was also measured. It was shown that the ratio of the alpha-rhythm frequency to parameters of the step-type behaviour of alpha oscillations positively correlated with memory performance.

Adult↗
PubMed1994

[Specifics of the formation of the alpha rhythm in different areas of the cerebral cortex in young children].

The age-specific features of distribution of capacity density values of modally specific monoherz components of optic alpha-rhythm and their response rearrangements to light stimulus suggest that in 2-3-year-old children, alpha-rhythm appears as three monoherz segments in the range 6-9 Hz with their heterodirectional changes. At this age stage of brain functional maturation, the authors have identified the border of synchronous and spasmodic changes in the spectral coherent indices of bioelectric activity formation in the projection and associative regions of the brain, which corresponds to 14-15 months of life.

Age Factors↗
PubMed2005

Alpha rhythms in mild dements during visual delayed choice reaction time tasks: a MEG study.

Can simple delayed response tasks affect latency and amplitude of magnetoencephalographic midline alpha rhythms (6-12 Hz) in early dementia? We recruited 15 mild Alzheimer's disease (AD) and 10 vascular dementia (VaD) patients (paired mini mental state exam of 17-24). The control groups comprised 18 young and 22 elderly normal subjects. In the first task, a simple "cue" stimulus (one bit) was memorized along a brief delay period (3.5-5.5s) up to a "go" stimulus triggering (right or left) button press. In the second task, the "cue" stimulus remained available along the delay period. Event-related reduction in power of the alpha rhythms indexed the cortical activation (event-related desynchronization, ERD) for the trials associated with correct behavioral responses. Behavioral performances to both tasks were lower in the AD and VaD patients than in the normal subjects. In particular, just four AD and five VaD patients executed a sufficient amount of correct responses for the alpha ERD analysis, so they were included in a unique group. In both tasks, the alpha ERD peak was later in latency in the demented and normal elderly subjects than in the normal young subjects. Furthermore, the alpha ERD peak was stronger in amplitude in the demented patients than in the normal subjects. These results suggest that simple delayed response tasks during physiological recordings are quite difficult for patients even at an early dementia stage. Such difficulty may induce the abnormal amount of the related cortical activation in dementia as revealed by the alpha ERD.

Adolescent↗
PubMedDate not supplied

[Directed regulation of human alpha-rhythm using feedback].

Directed control of intensity of the alpha-rhythm in the somatosensory cortical regions was examined in 20 healthy subjects in conditions of combined (visual and auditory) feedback connection. An attempt has been made to single out by means of control experiments, the factors influencing in such conditions of external stimulation the brain bioelectrical activity. A study was made of the changes in effectiveness of biocontrol in multiple (five) sessions of training. Data are given on the dynamics of some vegetative functions in controlling brain biopotentials.

Adolescent↗
PubMed1987

[Characteristics of the frequency component of EEG alpha rhythm of patients with neurosis-like schizophrenia (based on spectral analysis data)].

In 20 patients with neurosis-like schizophrenia and in 10 healthy subjects the authors, using the spectral analysis, assessed the composition of the alpha-range of the baseline EEG and studied the peculiarities of the frequency components of alpha-rhythm in various states. The patients were characterized by multimodality of the baseline EEG. The patients (versus the normal subjects) presented significantly different types of response of the main frequency components of EEG alpha-rhythm to the hyperventilation test.

Adolescent↗
PubMed1993

Quantification of alpha rhythm desynchronization using the acceleration spectrum entropy of the EEG.

Desynchronization of the alpha rhythm is usually quantified as a loss of power in the alpha band. In this study we describe an alternative approach where desynchronization is characterized as an increase in the irregularity of the EEG signal. A new measure, the acceleration spectrum entropy (ASE), is used to quantify EEG irregularity. The ASE is the normalized information entropy of the amplitude spectrum of the second derivative of a time series. The ASE is a measure of the randomness or irregularity of a time series and ranges from 0 (straight line) to 100 (discrete random signal). The ASE was calculated for short EEG epochs under eyes closed and eyes open conditions in 15 subjects. There was a significant increase in ASE in the eyes open condition, reflecting an increase in EEG complexity. The ASE is a sensitive measure of EEG desynchronization.

Alpha Rhythm↗
PubMed2000

Magnetic source imaging in fixation-off sensitivity: relationship with alpha rhythm.

A patient in whom a variety of abnormal EEG findings can be elicited by elimination of central vision and fixation demonstrates fixation-off sensitivity. The underlying mechanisms of fixation-off sensitivity and its relationship with alpha rhythm remain unclear. To obtain a better understanding of this issue, we used a whole-head magnetoencephalograph to study an epileptic child with fixation-off sensitivity resulting in a 3-Hz, large-amplitude oscillation (300 microV) over the occipital regions on the EEG. Magnetic source localization revealed alpha activity around the calcarine fissure and surrounding parieto-occipital areas. Magnetic sources of abnormalities relating to fixation-off sensitivity, however, usually were located deeper in the brain, suggesting more extensively distributed sources, with involvement of the cingulate gyrus and the basomesial occipitotemporal region. Distributions of the sources of both types of activities show independent clusters but also an appreciable domain of overlap. Our findings indicate that abnormalities related to fixation-off sensitivity can emerge in thalamocortical networks, with larger and more anterior cortical distribution than those that generate alpha rhythm. Transition in the type of oscillation appears not only to depend on a change in cellular dynamics but also to be reflected in a different spatial distribution of the underlying neuronal networks.

Alpha Rhythm↗
PubMed1996

The alpha rhythm in the electroencephalogram: a theory based on a neurophysiological model.

A column in the cerebral cortex is made up of a group of neurons and is considered to be a functional unit. Previous work has suggested that a column has two separate levels of activity, and that only a few of the columns are at the high level of activity simultaneously. To keep this number within proper limits, it is necessary to have a regulating system that reduces the cortical excitability when the number tends to increase, and vice versa. In the present paper, it is proposed that these changes up and down in the excitability can explain the generation of the alpha rhythm in the electroencephalogram. Preliminary results show that a normal alpha rhythm of about 10 Hz can be generated when the number of columns with high activity is shifting between four and five. The duration of the high activity of a column is around 450 ms.

Alpha Rhythm↗
PubMed1988

Behaviour of the alpha rhythm in electroencephalograms of visually impaired children.

One hundred and thirty-eight electroencephalograms (EEGs) of 104 children with ocular visual loss were studied and the findings correlated with clinical information. Records of blind children without other neurological deficits did not contain posterior slowing or occipital spikes. The frequency, reactivity and regulation of alpha rhythm were affected only when vision was at the level of finger-counting. Therefore the EEGs of the majority of 'normal' visually impaired children showed normal alpha behaviour. Although most totally blind children's records lacked alpha, five had spontaneously appearing and disappearing alpha rhythm. The EEG is a valuable tool in the evaluation of visually impaired children, provided the findings are interpreted appropriately. The earlier theory that visual deprivation can cause electrical abnormalities over the visual cortex was not supported by these data.

Adolescent↗
PubMed1992

Age-related changes in occipital alpha rhythm of adults with Down syndrome.

A power spectral analysis was performed on occipital EEGs recorded from 36 Down Syndrome (DS) subjects aged 15 to 54 and compared with two control groups; 47 healthy volunteers (Control) and 42 mentally retarded people without DS (MR). The frequencies of occipital alpha rhythms of DS showed a significant inverse correlation with chronological age, while Control and MR did not. The average frequencies of DS were significantly low even in the youngest age-group in comparison with those of Control, and also decreased in the age-groups of 35 and older compared with MR. It was considered that a slowing of alpha rhythm was a manifestation of premature aging that occurred in the underdeveloped brains of DS.

Adolescent↗
PubMed2005

Human alpha rhythms during visual delayed choice reaction time tasks: a magnetoencephalography study.

Magnetoencephalography (MEG) includes fast and comfortable recording procedures very suitable for the neurophysiological study of cognitive functions in aged people. In this exploratory MEG study in normal young adults, we tested whether very simple short-term memory (STM) demands induce visible changes in amplitude and latency of surface alpha rhythms. Two delayed response tasks were used. In the STM condition, a simple cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). In the control (no short-term memory; NSTM) condition, the cue stimulus remained available along the delay period. To make extremely simple the tasks, the explicit demand was visuospatial but the retention could be also based on phonological and somatomotor coding. Compared to the control condition, the amplitude of the alpha 1 (6-8 Hz) ERD decreased in the left hemisphere, whereas the amplitude of the alpha 2 (8-10 Hz) and alpha 3 (10-12 Hz) event-related desynchronization (ERD) increased in right and left parietal areas, respectively. Furthermore, the latency of the alpha ERD peak was slightly but significantly (P < 0.05) later in STM compared to control condition. In conclusion, whole-head MEG technology and very simple STM demands revealed significant changes of human neuromagnetic alpha rhythms in normal young adults.

Adult↗
PubMed2006

[Nonlinear dynamics characteristics in alpha rhythm of scalp electroencephalogram].

In regard to the controls and schizophrenia EEGs, we have got alpha rhythm from three points of view and verified the nonlinearity of the three kinds of rhythms. The results show that neither normal EEG alpha nor patients EEG alpha have the typical nonlinear characteristics. Therefore, we could not blindly use the theories of nonlinear dynamics to analyze the rhythm of brain wave.

Alpha Rhythm↗
PubMed1982

Components of visual attentiveness in suppression of the occipital alpha rhythm.

This study examined whether either visual input or "attention" exerts an influence on the alpha rhythm beyond that produced by oculomotor maneuvers such as movement and fixation. Alpha-suppressive effects of an attentional "set" were demonstrated in subjects anticipating a response to an unknown visual stimulus in the dark. In a second condition, subjects moved their eyes laterally between two visual targets. When visual input was increased by interspersing additional lights between the targets, a significant increase in alpha suppression was observed beyond that produced by eye movement alone. In the third condition, subjects fixated on a point of light (to stabilize oculomotor influences across tasks) while adjacent points were displayed at random intervals. Attentional "demand" was varied by requiring subjects alternately to respond to these flashing lights or passively view them. Both tasks produced alpha block relative to baseline periods, but relative suppression did not differ between tasks.

Alpha Rhythm↗
PubMed2006

Long-term enhanced desynchronization of the alpha rhythm following tetanic stimulation of human visual cortex.

It had been shown previously that a photic tetanus induces LTP-like changes in the visual cortex, as indexed by an enhancement of the N1b component of the visual evoked potential, recorded non-invasively by electroencephalography. This potentiation was shown to last over 1 h. In the present study, the effect of a photic tetanus on oscillatory activity is investigated. EEGs were collected from eight healthy subjects in three conditions while visual checkerboards were displayed. Following baseline presentations in two conditions a lateralized visual tetanus was given, either to the left or right visual field, and in a third condition no tetanus was given. This was followed by a return to baseline presentations, both immediately after the tetanus/control block, and 1 h later. Enhanced event-related desynchronization (ERD) of the alpha rhythm lasting 1 h was seen following the photic tetanus over occipital electrodes. Because ERD of the alpha rhythm is thought to represent active cortex, these results suggest that the visual tetanus induces long-lasting cortical changes, with stronger neuronal assemblies and increased neuronal output.

Adult↗
PubMed1990

[Blocking of the alpha rhythm induced by sensory self-stimulation].

In a series of experiments in animals and in man several authors have shown that sensory stimulation induces low voltage fast activity in the EEG. The problem to be studied in this work is related to the EEG changes produced by self-stimulation. A group of human subjects were instructed to be self-stimulated with clicks and flashes of light randomly applied by themselves. When the subjects were with the eyes closed and in resting state, alpha rhythm was predominantly recorded in the EEG. However, during acoustic or visual stimulation a low voltage fast activity was predominantly observed in the EEG. In self-administration of the stimulus a low voltage fast activity was recorded in the EEG several seconds before the stimulus application. These results suggest that the activation of a complex neuronal mechanism involved in the volitive response, as well as anxiety and attentive states of the subject occurring before the actual stimulation to select the moment at which the stimulus has to be applied, can be responsible for the blocking of the alpha rhythm previously to the flashes of light and clicks presentation.

Acoustic Stimulation↗
PubMed1982

Reduction of variability of EEG occipital, parietal, and central alpha rhythms by visual feedback stimulation.

Two experiments, each with 24 normal right-handed adults, examined variability of the response of EEG alpha rhythms during repeated visual stimulations that were contingent on the occurrence of those rhythms. Within-trial variability of alpha durations and no-alpha (alpha blocking) durations were recorded from bipolar derivations along two bilateral posterior-anterior lines. Variability was significantly lower for: (1) the contingent EEG connected to the stimulus compared to the contralateral EEG, which was recorded simultaneously but was not connected to the stimulus; (2) occipitoparietal EEGs compared to parietocentral EEGs; (3) alpha durations compared to no-alpha durations. Differences in variability among the four EEG locations on the left or the right side were significant for contingent EEGs but not for contralateral nonconnected EEGs. The results were interpreted to be a demonstration that feedback EEG method can be applied to research on the functional topography of an EEG response to sensory stimuli in terms of the reduction of variability of the response that can be achieved with feedback.

Adolescent↗
PubMed1993

Alpha rhythm in the cat thalamus.

In cats, electrocortical rhythms at about 10 Hz displaying common characteristics with the human alpha rhythm [1] were recorded from the part of the visual cortex that includes the anterior half of areas 17 (on the cortical convexity), of area 18 and of their common limit, representing the projection of the lower contralateral visual quadrant and that of the lower vertical meridian. It is shown here that activities highly correlated with these rhythms and at the same frequency, were recorded from the anterior half of the laminar dorsal lateral geniculate body (mediodorsal part of layer A), and also from a limited area medial to this nucleus. The cat thalamocortical alpha system thus appears to concern only the projection of the lower quadrants, probably excluding the area centralis itself.

Alpha Rhythm↗