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

Alpha-contingent EEG feedback reduces SPECT rCBF variability

EEG feedback methods, which link the occurrence of alpha to the presentation of repeated visual stimuli, reduce the relative variability of subsequent, alpha-blocking event durations. The temporal association between electro-cortical field activation and regional cerebral blood flow (rCBF) led us to investigate whether the reduced variability of alpha-blocking durations with feedback is associated with a reduction in rCBF variability. Reduced variability in the rCBF response domain under EEG feedback control might have methodological implications for future brain-imaging studies. Visual stimuli were randomly presented to seven subjects, contingent upon the occurrence of alpha (alpha-contingent stimulation (ACS)) or alpha-blocking (not-alpha-blocking-contingent stimulation (NACS)) events. We employed a within-subjects design. rCBF was measured from multiple, cortical and sub-cortical regions. The primary dependent variables were the Mean, Standard Deviation and the ratio of Mean/Standard Deviation of: 1) the alpha-blocking response durations and 2) the temporally summated rCBF responses within the Visual Associative regions of interest (ROIs). Additional within-subjects rCBF measures were derived to quantify the variance-reducing effects of ACS across multiple, distributed areas of the brain. Both EEG and rCBF measures demonstrated decreased variability under ACS. This improved control was seen for localized as well as anatomically distributed rCBF measures.

Human EEG, behavioral stillness and biofeedback

This theoretical synthesis affirms that the normal human EEG is: (1) an indicator of movements of behavior; (2) an undifferentiated indicator of cortical work; but (3) not an indicator of mental processes. A majority of cortical work for an awake person is the mobilization and regulation of all the processes involved in the production, control and prediction of movements of behavior. Abundant synchronous slow waves (alpha, mu, sensory-motor rhythm) indicate a demobilization of voluntary and reflexive, phasic neuromuscular processes which predict, initiate, regulate, and terminate voluntary behavior and movement with a corresponding reduction of afferent feedback associated with sensory data capture, sensory motor integration and behavior. Cortical theta in association with drowsiness indicates that there is further demobilization of reflexive, synergistic, neuromuscular process (as for gait, defensive responses, anti-gravity support), and a reduction of tonic processes which maintain muscle tone or tension with concomitant further reduction of afferent feedback. These various states of behavioral stillness are the catalyst of beneficial psychological and behavioral processes which have been observed to follow biofeedback training to increase synchronous EEG rhythms, and may provide a therapeutic context for psychotherapeutic interventions.

Alpha-contingent stimulation with binocular and monocular viewing

The method of alpha-contingent stimulation was evaluated under conditions of (1) binocular viewing, (2) monocular viewing, dominant eye, and (3) monocular viewing, non-dominant eye. Twelve normal young adults with normal vision and unequivocal alpha rhythms were tested. There was no evidence against generalizing the alpha contingent stimulation (ACS) method to monocular modes of viewing. The same methodological advantages, e.g. reduced random variability of the latency and duration of alpha blocking, were observed for all modes of viewing, which extends the range of possible applications of ACS method.

Detection of cerebral lateralization of function using EEG alpha-contingent visual stimulation II

The replicative reliability of durations of alpha-blocking following visual stimulation over different cortical sites was assessed with the method of alpha-contingent stimulation. Fourteen right-handed undergraduates were tested in a randomized factorial design. Words or geometric designs of equal luminance were presented by computer to randomly selected visual half-fields contingent on the occurrence of alpha at one of 4 placements (left and right occipital and left and right temporal). The control (mean/s) of alpha-blocking durations was significantly greater for contralateral visual half-field stimulation compared to ipsilateral visual half-field stimulation. This and other results were interpreted in terms of the concept of replicative reliability of retinal-cortical connections to occipital and temporal lobes and affirm the validity and sensitivity of the method.

Effect of alertness and visual attention on optokinetic nystagmus in humans

The effect of alertness and visual attention on optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) was studied in 20 volunteers. Electroencephalographic (EEG) activity was recorded over the occipital lobe. Exposure to sound and vibration caused a significant increase in the mean slow-phase velocity of OKN, whereas its maximum slow-phase velocity remained unaffected. Vibration tended to increase the mean slow-phase velocity of OKN more than sound did, though the difference was not statistically significant. Vibration also significantly increased the OKAN. When alpha rhythm appeared in the occipital EEG during OKN, the velocity of concurrent slow phases was reduced. However, the periods of alpha rhythm did not differ between the different stimulus conditions. The findings suggest that sound and vibration activate the subcortical optokinetic mechanism, thus causing an increase in the mean velocity of OKN. Abatement of visual attention is reflected in temporary reduction of OKN in conjunction with the appearance of alpha waves and is to be interpreted as transient quiescence of the cortical optokinetic mechanism.

Attention and regulation of EEG alpha-attenuation responses

Two experiments with 16 normal adults of both sexes tested the hypothesis that inattention to a biofeedback display is associated with increased variability of those physiological processes that had been regulated by the biofeedback. Each experiment was a repeated-measures-on-independent-subjects-design. Dependent variables were the time durations and the mean rms power of two mutually exclusive segments of the parietal-occipital EEG: alpha and not-alpha segments. Independent variables were combination of counting tasks and instructions to look at, listen to, and count visual and auditory flashes and clicks. The durations of alpha and not-alpha segments were controlled or regulated by means of an alpha-contingent visual feedback stimulus, Attention to the feedback stimulus was challenged by instructions to count other, noncontingent stimuli. Control of alpha and not-alpha segments was least for conditions of (1) "sham" feedback, and (2) feedback with instructions to count noncontingent auditory clicks, which were presented 3/sec while the feedback visual stimuli were occurring. A new EEG test of attention and distraction was suggested.