Dipole sources of the human alpha rhythm

Summary Dipole sources were investigated in 22 normal subjects with a variety of strategies available through the BESA program. When all the data were summed one regional source, located near the midline in the basal portions of the occipital lobe, explained 92% of the variance. Two regional sources, initially constrained for symmetry but subsequently freed from constraint placed them also in the occipital regions near the midline and reduced the residual variance to 4%. Pooled data obscure, however, the marked individual differences especially in regard to lateralization. In the individual case the major source was also always in one occipital area but its location, especially the degree of separation from the midline depended upon alpha distribution and the strategy used in the workup of the data. The orientation of the major components of the regional sources was usually in the posterior-anterior direction, fairly parallel to the midline and while the other one pointed to the upper convexity. Because of the considerable variability of the alpha rhythm in given subjects and even within the same individual a model which requires symmetry constraints is not optimal for all instances, even when constraints are lifted thereafter. The study demonstrated the feasibility of distinguishing predominantly mesial sources from those which are bihemipheric with more lateral origins but several different models may have to be used to reach the most realistic conclusions.The authors would like to express their appreciation to Dr. Michael Scherg for his help and advice.     

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.     

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.     

EEG alpha rhythm, intention and oculomotor control.

A replication of Wertheim's (1981) visual pursuit tracking study examined the reactivity of the posterior EEG alpha rhythm to two tracking tasks. Twelve subjects visually tracked a light spot moving in a predictable or an unpredictable path. The EEG was recorded from O1, O2, P3, P4, T5, and T6, referenced to linked mastoids, and power for the alpha frequency band was calculated for 60 s trial epochs. Results showed significantly higher occipital and posterior temporal alpha power during the predictable tracking trials in agreement with Wertheim's findings. The significance of this for his attention/intention model is discussed.     

Revisiting the eye opening response of the Glasgow Coma Scale

The Glasgow Coma Scale (GCS), introduced by Teasdale and Jenneth in 1974, has received tremendous acclaim from clinicians and has been extensively used in clinical practice for the evaluation of the level of consciousness. The author notes that some traumatic brain injury patients close eyes in response to painful stimuli as opposed to the eye opening response to pain of the GCS. A revision of the eye opening response subsection of the GCS is suggested.     

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.     

Interhemispheric changes in alpha rhythm related to time perception

Each cerebral hemisphere processes environmental information in a different but complementary manner. Structures located in the left hemisphere are assumed to participate in symbolic-logic thinking. Time perception may be considered among such thinking processes. The present study evaluates bilateral occipito-central EEG activity in healthy, right-handed subjects which was produced while they performed a visuomotor monitoring task. The task consisted of two stages. The first stage involved the subject's learning a fixed time interval (10 sec) and the measurement of their reaction time. Subjects responded to an isolated light stimulus by pressing a button with the dominant hand. In the second stage, the subjects accuracy in estimating interval-length was evaluated. Two forms of EEG analysis were used, frequency and alpha ratio, each of which was measured both prior to and subsequent to the motor response. A reversal group was used to carry out a complementary test. Subjects responded in the first block of experiments with the non-dominant (left) hand and with the dominant hand in the second. Results showed that left hemisphere activity was continuous during the interval-learning stage and with optimal reaction times and remained continuous when estimation values approximated the real interval. In addition, in optimal reaction time and near to optimal time estimation responses, the left side showed lower frequency and alpha ratio than did the right. Finally a progressive enhancement in both parameters from the right hemisphere was related to deterioration in test performance. Results from the reversal group did not differ from those of the first group. As evaluated by gross measurements of the EEG, a predominant participation of the left hemisphere in time processing is concluded.     

Experience-dependent binocular competition in the visual cortex begins at eye opening

Visual experience begins at eye opening, but current models consider cortical circuitry to be resistant to experience-dependent competitive modification until the activation of a later critical period. Here we examine this idea using optical imaging to map the time course of receptive field refinement in normal mice, mice in which the contralateral eye never opens and mice in which the contralateral eye is silenced. We found that the refinement of ipsilateral eye retinotopy is retarded by contralateral deprivation, but accelerated by silencing of the contralateral eye. Patterned visual experience through the ipsilateral eye is required for this acceleration. These differences are most obvious at postnatal day 15, long before the start of the critical period, indicating that experience-dependent binocular plasticity occurs much earlier than was previously thought. Furthermore, these results suggest that the quality of activity, in terms of signal to noise, and not the quantity, determines robust receptive field development.     

Myelination in rabbit optic nerves is accelerated by artificial eye opening

Artificial opening of the eyes of young rabbits on the 5th postnatal day led to accelerated myelination: the myelin-specific basic and proteolipid proteins nearly doubled between the 7th and the 10th postnatal days when compared to controls; 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) activity also increased by about 60%. Conversely, lowered AChE activities presumably reflected elevated myelin/axolemma ratios. Myelination in treated animals normalized during later ontogenetic stages (greater than 20th postnatal day).     

Receptive field center size decreases and firing properties mature in ON and OFF retinal ganglion cells after eye opening in the mouse

Development of the mammalian visual system is not complete at birth but continues postnatally well after eye opening. Although numerous studies have revealed changes in the development of the thalamus and visual cortex during this time, less is known about the development of response properties of retinal ganglion cells (RGCs). Here, we mapped functional receptive fields of mouse RGCs using a Gaussian white noise checkerboard stimulus and a multielectrode array to record from retinas at eye opening, 3 days later, and 4 wk after birth, when visual responses are essentially mature. Over this time, the receptive field center size of ON and OFF RGC populations decreased. The average receptive field center size of ON RGCs was larger than that of OFF RGCs at eye opening, but they decreased to the same size in the adult. Firing properties were also immature at eye opening. RGCs had longer latencies, lower frequencies of firing, and lower sensitivity than in the adult. Hence, the dramatic maturation of the visual system during the first weeks of visual experience includes the retina.     

Changes in alpha rhythm asymmetry during learning of verbal and visuospatial tasks.

Alpha activity in the two cortical hemispheres was examined during learning and overlearning of a verbal and a visuospatial task. Compared to a pretask baseline condition, the amount of alpha activity during the tasks was decreased. An increase in alpha activity was found from learning to overlearning in both tasks. A greater amount of alpha was found in the right hemisphere for both tasks. In addition, no difference in the degree of alpha asymmetry was found between the tasks. This was discussed in light of prior contrary findings. A significant positive correlation was found between change in learning rate and change in alpha asymmetry during the verbal task. An interpretation of this finding was offered in terms of the level of hemispheric activation reflecting the degree of task engagement.     

Immediate effects of alpha/theta and sensory-motor rhythm feedback on music performance

This is one of a series of investigations comparing two EEG-neurofeedback protocols – Alpha/theta (A/T) and Sensory-Motor Rhythm (SMR) – for performance enhancement in the Arts, here with the focus on music. The original report (Egner and Gruzelier, 2003) established a beneficial outcome for elite conservatoire musicians following A/T training in two investigations. Subsequently this A/T advantage was replicated for both advanced instrumental and novice singing abilities, including improvisation, while SMR training benefited novice performance only (Gruzelier, Holmes et al., 2014). Here we report a replication of the latter study in university instrumentalists who as before were novice singers with one design change — post-training performances were conducted within the tenth final session instead of on a subsequent occasion. As before expert judges rated the domains of Creativity/Musicality, Communication/Presentation and Technique. The proximity to training of the music performances within the last session likely compromised gains from A/T learning, but perhaps reinforced the impact of SMR training efficacy. In support of validation there was evidence of strong within- and across-session A/T learning and positive linear trends for across-session SMR/theta and SMR/beta-2 ratio learning. In support of mediation learning correlated with music performance. The A/T outcome was markedly discrepant from previous studies and should dispel any impression that the hypnogogic state itself is transferred to the performance context. The effects of SMR ratio training are consistent with an impact on lower-order abilities required in novice performance such as sustained attention and memory, and benefiting all three domains of music assessment.