Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Alpha Rhythm”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 19 recordsLinked to original sources
PubMed1997

Segregation of the thalamic alpha rhythms from cortical alpha activity using the Savit-Green S-statistic and estimated correlation dimension.

The large-amplitude, occipital alpha rhythm of the human electroencephalogram (EEG) is associated in normal subjects with a state of relaxed wakefulness. We analyzed resting eyes-open and eyes-closed human EEG data using three measures: power in the 8-12-Hz alpha frequency band, estimated correlation dimension (D2), and the Savit-Green S-statistic. At occipital loci, two groups of points were evident in the scatterplot of S vs. estimated D2. Group A was of higher dimension and consisted of predominantly eyes-open records. Group B was of lower dimension and consisted of more eyes-closed than eyes-open records. Furthermore, Group B had a broad range of alpha power, with alpha power being negatively correlated with estimated D2 (higher alpha power associated with lower dynamical complexity). In contrast, Group A had a very small range of low alpha power, and was positively correlated with estimated D2 (higher alpha power associated with increased dynamical complexity). Our results indicate that Group B EEG (the alpha rhythm) and Group A EEG (EEG containing 'other' alpha activity) have fundamentally different dynamical properties.

Adult↗
PubMed1984

Alpha rhythm and alpha-like activity in coma.

A normal waking EEG was obtained on a 22 year old man four days prior to cardiopulmonary arrest. Three days after resuscitation the EEG showed the pattern of alpha-like activity while the patient remained in deep coma. Since the EEGs were recorded by the same technician using the same 16 channel electroencephalograph and montages, it is possible to compare in the same individual these alpha-frequency activities before and after arrest. The alpha-like activity of coma does not resemble the waking alpha rhythm in amplitude, frequency, spatial distribution, variability and reactivity.

Adult↗
PubMed2002

Simultaneous EEG and fMRI of the alpha rhythm.

The alpha rhythm in the EEG is 8-12 Hz activity present when a subject is awake with eyes closed. In this study, we used simultaneous EEG and fMRI to make maps of regions whose MRI signal changed reliably with modulation in posterior alpha activity. We scanned 11 subjects as they rested with eyes closed. We found that increased alpha power was correlated with decreased MRI signal in multiple regions of occipital, superior temporal, inferior frontal, and cingulate cortex, and with increased signal in the thalamus and insula. These results are consistent with animal experiments and point to the alpha rhythm as an index of cortical inactivity that may be generated in part by the thalamus. These results also may have important implications for interpretation of resting baseline in fMRI studies.

Adult↗
PubMed1997

Normal and pathological changes in alpha rhythms.

Normal alpha rhythm begins to appear at three months. It was possible to observe successively, the rhythmicity, visual reactivity, occipital topography, and at the end of the first year, the first bursts of 7-8 Hz waves. Evolution of alpha was not linear with the age. Alpha frequency acceleration was important before the age of 11 years. In adults it decreased from 20 to 55, then there was a tendency to increase with aging. Amplitude was highest at 11-12 years, then its tendency was to decrease until 40, and to increase later. In pathology, for instance, alpha could be observed too early in newborn and infants with malformations, in children, in some psychiatric diseases, in adults and old people, alpha was replaced by theta waves in dementia: it seemed to be a very reliable sign, at the beginning of the disease.

Adolescent↗
PubMed1997

Study of human occipital alpha rhythm: the alphon hypothesis and alpha suppression.

Alpha rhythm of the parieto-occipital area is comprised of a parade of short-lived cortical excitations (alphons), each of which exhibits oscillations having a stable period within the alpha bandwidth. Strong alpha rhythm is produced by alphons extending over a larger cortical area, although an enhanced cortical current density may also contribute. Local suppression of alpha rhythm indicates when specific cortical areas become engaged in sensory or cognitive functions. Examples are provided for mental imagery, visual memory, auditory memory, and silent rhythming.

Alpha Rhythm↗
PubMed1988

The cerebral origin of the alpha rhythm.

The EEG alpha rhythm was recorded from 8 isolated canine brains in the absence of orbital contents, drug effect, or pulsatile cerebral blood flow. Abrupt shift to hypoxic perfusion, with maintenance of other perfusion variables, resulted in a loss of alpha coincident with a fall in CMRO2 and rise in oxygen deficit. It is concluded that the alpha rhythm reflects neural electrical activity, and that sources in the eye muscles or in cardiac-induced electromechanical properties of the brain may be rejected.

Alpha Rhythm↗
PubMed1992

Alpha rhythm and the pineal gland.

Alpha rhythm is classically described as a bilateral posterior rhythm of substantially constant frequency in the range of 8-13 Hz which is enhanced by mental relaxation and blocked by attention. Since the full expression of alpha rhythm has been shown to occur coincident with puberty, it is possible that the establishment of alpha rhythm is subject to neuroendocrine influences which govern psychosexual maturation. There is ample evidence to indicate that the pineal gland is implicated in cerebral maturation and psychosexual development. Nocturnal plasma melatonin levels have been shown to decline progressively throughout childhood reaching a nadir at puberty. Since administration of melatonin has been reported to block alpha rhythm, it is proposed that the progressive decline in melatonin secretion during childhood facilitates the maturation of the alpha rhythm. Consequently, the presence of alpha rhythm could be used as a neurophysiological marker for the activity of the pineal gland and disorders associated with absent or delayed maturation of the alpha rhythm such as autism, dyslexia, personality disorders, epilepsy, Tourette's syndrome, and schizophrenia might be related to disturbances of pineal melatonin functions in early life. Moreover, since the EEG patterns associated with cerebral immaturity (i.e., slowing, absence of alpha activity) are more pronounced in the left hemisphere, this hypothesis implies differential influence of the pineal gland on hemispheric maturation potentially accounting for the vulnerability of the left hemisphere to cerebral insults.

Alpha Rhythm↗
PubMed1975

Ongoing occipital rhythms and the VER. I. Stimulation at peaks of the alpha-rhythm.

As a first step toward determining the source of variability in the visually evoked response (VER) between subjects, we have examined the relationships between the VER and the alpha-rhythm. This was done by comparing the VER's to photic stimuli delivered at positive and negative peaks of the alpha-rhythm (alpha-synchronized stimuli) with VER's to flashes delivered at a fixed interval, unsynchronized with the alpha-rhythm. Average VER's for the three classes of stimuli were calcuated for each of ten subjects. In addition, a grand average VER (GVVER) WAS CALCULATED FOR EACH STIMULUS CLASS BY AVERAGING THE INDIVIDUAL AVERAGE VER's. Quantitative comparisons between GVER's were made using cross- correlograms. Cross-correlograms were calculated between each of the GVER's, and between the GVER's to alpha-synchronized stimulation and their controls. These data show that the first 120 msec. poststimulus interval of the Gver's to alpha-synchronized stimulation are highly correlated with the prestimulus alpha- rhythm. The data also show a component occurring in al GVER's which is independent of the alpha-rhythm. This component begins 120 msec. After stimulation, reaches peak amplitude at 200 msec, and decays to baseline at 240 msec. Thses findings suggest that much of the variability in VER recordings may be due to alpha-activity which has been insufficiently attenuated by averaging.

Adult↗
PubMed1997

Alpha rhythms: noise, dynamics and models.

Alpha rhythms appear as sinusoidal-like oscillations in the electroencephalogram (EEG) within the frequency range 8-12 Hz that waxe and wane in a more or less irregular way. The irregularity may have various origins. It may be due to noise or the oscillations may have an intrinsic irregular character, e.g. they may be generated by chaotic processes [Jansen (1991) Quantitative analysis of electroencephalograms: is there chaos in the future? Int. J. Biomed. Comput., 27: 95-123; Pradham, N. and Dutt, D.N. (1993) A nonlinear perspective in understanding the neurodynamics of EEG. Comput. Biol. Med., 23: 425-442; Pritchard et al. (1995) Dimensional analysis of resting human EEG II: Surrogate-data testing indicates nonlinearily but not low-dimensional chaos. Psychophysiology. 32: 486]. The term noise is often used in neurophysiology with different connotations as pointed out by Bullock (1990), either meaning an unwanted signal from the point of view of the receiver of a message, or a signal with intrinsic random fluctuations, i.e. with a stochastic character. Here we consider noise in this sense, as random or quasi-random neural activity. In this overview, we concentrate on the question of whether alpha rhythms should be considered generated in neuronal networks (1) as forms of filtered noise, (2) as deterministic oscillations influenced by noise or (3) as the result of chaotic dynamics. A clear answer to this question can have theoretical value because it may lead to a general model of the generation of this important EEG signal. Such a model, of course, would be a macroscopic one, since it would primarily account for the properties of the alpha rhythms at the neuronal network level. A translation of these properties to the microscopic, i.e. neuronal, level will not be easy to achieve without more direct knowledge of the membrane and synaptic basic properties of the neurons involved. Here we consider the question formulated above by presenting some relevant experimental evidence and theoretical arguments. The consideration whether alpha rhythms may have noise or chaotic sources implies examining how and where such sources can occur in the neuronal networks of the brain. Therefore we present, first, some basic data regarding the possible origin of noise and of chaos in neuronal networks. Second, the signal analysis methods that have to be applied in order to discriminate between filtered noise activities and chaotic oscillations are introduced. Third, the implications of these signal analyses regarding the possible answer to the initial question are discussed.

Alpha Rhythm↗
PubMed2001

Multiplicity of the alpha rhythm in normal humans.

Previous analyses of the alpha rhythm in a given single derivation have shown that it is a result of narrowband filtration of a broadband process. As many as three distinct alpha rhythms within each hemisphere could be differentiated in 65 resting, awake subjects by considering the spatial properties of these rhythms along with their dynamics. The analysis was based on cross-correlation measurements of rhythmic and broadband processes, and comparison of the dynamic characteristics of oscillatory systems underlying the alpha rhythms. Five-minute epochs of the EEG were recorded to provide 10% precision of the statistical estimates of the variables measured. A frontal alpha rhythm independent of occipital rhythmic activity was present in 20% of subjects. This third rhythm is distinct from the more familiar alpha and mu rhythms described in the literature, and is attenuated when the eyes are open. The authors demonstrate that the dynamic characteristics of the oscillatory systems underlying the alpha rhythm, as well as intrahemispheric coefficients of cross-correlation, are reproducible over time in a single subject. These parameters can form the basis for reliable individual EEG characteristics in the description of the "normal" EEG. The high correlation of the alpha rhythm in symmetric derivations could be explained by symmetric afferent impulse flows rather than by structural interconnection between the oscillatory systems.

Adult↗
PubMed1980

EEG changes induced by light stimuli modulated with the subjects alpha rhythm.

A new method, named the 'alpha wave modulated light' (AML) stimulation, has been used for controlling the frequency of sine wave modulated light by the subject's on-going alpha rhythm. The EEG was recorded from O1 and O2. With the AML stimulation using either the left occipital alpha rhythm or the right, two phase differences of O degrees and 180 degrees were created between AML and the alpha rhythmn. The peak frequency and power of occipital alpha in both hemispheres and the coherence and phase between the left and right occipital EEG were obtaned for 7 subjects. The alpha power was larger at a 180 degrees phase shift than at a 0 degrees phase shift with ipsilateral AML stimulation. The ipsilateral increase in the alpha power was greater than the contralateral at a 180 degrees phase shift. Larger coherence value and right phase lead were observed at 180 degrees phase shift by use of the right alpha rhythm. The possible mechanisms of influences of AML stimulation on the alpha activity were discussed.

Adolescent↗
PubMed2006

Influence of seamlessness between pre- and poststimulus alpha rhythms on visual evoked potential.

The influence of seamlessness between the prestimulus alpha rhythm and poststimulus alpha ringing on the visual evoked potentials (VEPs) was investigated. Subjects passively viewed a series of 1000 flash stimuli with their eyelids closed, and their VEPs were recorded. The instantaneous phase angle of the alpha rhythm in each subject was calculated by using a two-cycle complex exponential sequence. VEPs were classified into four subsets according to seamlessness: how well the phase angle of the prestimulus alpha rhythm and the backward-extrapolated phase angle from poststimulus alpha ringing were synchronized. VEPs of each subset were averaged. A one-way repeated measures analysis of variance revealed that seamlessness significantly affected the amplitude of P100. Moreover, the level of seamlessness significantly affected the phase locking index. Two models for the generating evoked potentials have been proposed; one is the phase resetting model (Makeig, S., Westerfield, M., Jung, T.P., Enghoff, S., Townsend, J., Courchesne, E., Sejnowski, T.J., 2002. Dynamic brain sources of visual evoked responses. Science 295, 690-694) and the other is the evoked model (Mäkinen, V., Tiitinen, H., May, P., 2005. Auditory event-related responses are generated independently of ongoing brain activity. Neuroimage 24, 961-968). These results suggest that alpha ringing is possibly generated by the phase-resetting alpha rhythm and support the phase resetting model.

Adult↗
PubMed2004

Cortical and subcortical correlates of electroencephalographic alpha rhythm modulation.

Neural correlates of electroencephalographic (EEG) alpha rhythm are poorly understood. Here, we related EEG alpha rhythm in awake humans to blood-oxygen-level-dependent (BOLD) signal change determined by functional magnetic resonance imaging (fMRI). Topographical EEG was recorded simultaneously with fMRI during an open versus closed eyes and an auditory stimulation versus silence condition. EEG was separated into spatial components of maximal temporal independence using independent component analysis. Alpha component amplitudes and stimulus conditions served as general linear model regressors of the fMRI signal time course. In both paradigms, EEG alpha component amplitudes were associated with BOLD signal decreases in occipital areas, but not in thalamus, when a standard BOLD response curve (maximum effect at approximately 6 s) was assumed. The part of the alpha regressor independent of the protocol condition, however, revealed significant positive thalamic and mesencephalic correlations with a mean time delay of approximately 2.5 s between EEG and BOLD signals. The inverse relationship between EEG alpha amplitude and BOLD signals in primary and secondary visual areas suggests that widespread thalamocortical synchronization is associated with decreased brain metabolism. While the temporal relationship of this association is consistent with metabolic changes occurring simultaneously with changes in the alpha rhythm, sites in the medial thalamus and in the anterior midbrain were found to correlate with short time lag. Assuming a canonical hemodynamic response function, this finding is indicative of activity preceding the actual EEG change by some seconds.

Acoustic Stimulation↗
PubMed1975

Somatic evoked response components and recovery functions in subjects with mu and alpha rhythms.

Subjects with prominent rolandic mu and alpha rhythms showed similar late somatic evoked response (SER) components but different SER recovery functions. A late P5x component was present when SER were superimposed on mu and alpha rhythms spontaneously recorded from the rolandic region of inattentive individuals. Since P5x was not present in other inattentive subjects unless SER were superimposed on a rhythmic rolandic activity evoked by an attentive situation, it seems reasonable to assume that the P5x component is partially due to spontaneous or evoked rolandic EEG rhythmicity. In addition, single propioceptive stimuli produced blocking of mu rhythm and a flat recovery function of the P5a component. In contrast, similar stimuli produced an enhancement of alpha rhythm and a periodic amplitude modulation curve of the P5a component. These results suggest that the P5a component is mediated by the same neurophysiological mechanisms which block or modulate the spontaneous rolandic EEG rhythms.

Adolescent↗
PubMed2000

Decomposition of posterior alpha rhythm.

The classical posterior alpha rhythm has been decomposed into regular and irregular components using orthogonal transformation. A periodicity generator is considered, which has three characteristic control parameters: the periodicity, the amplitudes or scaling factors and the pattern associated with successive periodic segments. The regular component is shown to be equivalent to an oscillator or periodicity generator whose parameters are dynamically varying and, thus, producing both amplitude- and frequency-modulation. The irregular component is devoid of such modulating behavior. Electroencephalogram signals from normal, maniac and epileptic subjects are studied. Through analytic signal-based analysis, it is shown that for the regular component, healthy brain possesses universal scaling behavior, whereas heterogeneous scaling or absence of universality is observed for the diseased brain.

Adolescent↗
PubMedDate not supplied

[Dipole models of alpha-rhythm generators].

Different hypothesis of the alpha rhythm origin were tested by dipole simulation of the alpha rhythm sources. EEG was recorded during driving photic stimulation in order to increase the signal-to-noise ratio. Models with fixed and moving dipoles were analyzed. Dipole sources were compared with magnetic resonance imaging (MRI) scans to find the exact location of oscillations in brain anatomical structures. A two-level multiple dipole model was found to fit the EEG most adequately. The first level was represented by two oscillators localized in the thalamic reticular nuclei, and the second level is associated with two modality-specific oscillators localized in the respective cortical areas.

Adult↗
PubMed1997

Alpha rhythms as physiological and abnormal phenomena.

There are three physiological alpha rhythms in mature healthy humans: (a) the classical posterior alpha; (b) the Rolandic mu rhythm and (c) the midtemporal 'third rhythm'. The classical posterior alpha rhythm develops out of a 4/s rhythm appearing at age 4 months and gradually reaches the alpha frequency band around age 3 years. The mature frequency around 10/s is subject to subtle physiological changes and grossly decelerates in the face of pathology. No posterior alpha rhythm may be detectable in a minority of healthy adults with an inherited low voltage fast EEG. One is tempted to speculate that these individuals may have a hidden alpha rhythm in neuronal level and defective mechanisms of synchronization. Alpha blocking with visual stimuli (eye opening) is a classical response; responses to mental stimuli (mental arithmetic) are inconsistent, presumably due to the involvement of higher cognitive functions. The Rolandic my rhythm is found with scalp EEG in a minority of subjects but there is good reason to presume that all healthy adults have this rhythm. A particularly powerful mu rhythm reaches the scalp but this could be also an indicator of a mild CNS dysfunction. There is even a relationship between mu rhythm and the central spike activity in children with benign Rolandic epilepsy. The midtemporal third rhythm is not detectable in the scalp EEG unless there are local bone defects. Its functional significance is debatable; its blocking responses encompass various higher cognitive tasks and are inconsistent; responses to auditory stimuli do occur but appear to be of secondary significance. This rhythm arises from midtemporal structures which by far exceed the borders of the auditory cortex. Abnormal rhythmical alpha activity-above all the alpha coma in life-threatening cerebral anoxia -is discussed in order to deepen our understanding of the physiological alpha rhythms. Severe cortical de-afferentation may give rise to cortical autorhythmicity-either in alpha frequency or in other frequency bands. Physiological alpha rhythms are likely to have closer relationships to 'events' than one might have thought earlier. The demonstration of event-related desynchronization and synchronization (in Pfurtscheller's work) clearly underscores this view.

Alpha Rhythm↗
PubMed2003

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

The numbers of alpha-rhythm equivalent current dipoles (ECD) arising in the human brain before and during rhythmic photostimulation at the alpha-rhythm frequency was studied in six healthy adult subjects. Dipoles were calculated using a single-dipole model for the whole of the alpha-range and three subranges by solution of inverse equations in a three-layer model of the head obtained by simultaneous use of EEG data and MRI tomograms of the subjects' heads. The number of apparent ECD was significantly associated with rhythmic photostimulation and depended on the phase of the alpha-rhythm wave at which stimulation started and on the type of visual illusion (circle, spiral, grid) appearing during this time. The relationship between these data and the hypothetical wave process scanning the human visual cortex at the frequency of the alpha-rhythm is discussed.

Adolescent↗