EEG alpha activity influenced by visual input and not by eye position

Synchrony and Complexity in State-Related EEG Networks: An Application of Spectral Graph Theory

The brain may be considered as a synchronized dynamic network with several coherent dynamical units. However, concerns remain whether synchronizability is a stable state in the brain networks. If so, which index can best reveal the synchronizability in brain networks? To answer these questions, we tested the application of the spectral graph theory and the Shannon entropy as alternative approaches in neuroimaging. We specifically tested the alpha rhythm in the resting-state eye closed (rsEC) and the resting-state eye open (rsEO) conditions, a well-studied classical example of synchrony in neuroimaging EEG. Since the synchronizability of alpha rhythm is more stable during the rsEC than the rsEO, we hypothesized that our suggested spectral graph theory indices (as reliable measures to interpret the synchronizability of brain signals) should exhibit higher values in the rsEC than the rsEO condition. We performed two separate analyses of two different datasets (as elementary and confirmatory studies). Based on the results of both studies and in agreement with our hypothesis, the spectral graph indices revealed higher stability of synchronizability in the rsEC condition. The k-mean analysis indicated that the spectral graph indices can distinguish the rsEC and rsEO conditions by considering the synchronizability of brain networks. We also computed correlations among the spectral indices, the Shannon entropy, and the topological indices of brain networks, as well as random networks. Correlation analysis indicated that although the spectral and the topological properties of random networks are completely independent, these features are significantly correlated with each other in brain networks. Furthermore, we found that complexity in the investigated brain networks is inversely related to the stability of synchronizability. In conclusion, we revealed that the spectral graph theory approach can be reliably applied to study the stability of synchronizability of state-related brain networks.

Effects of an Integrated Neurofeedback System with Dry Electrodes: EEG Acquisition and Cognition Assessment

Electroencephalogram (EEG) neurofeedback improves cognitive capacity and behaviors by regulating brain activity, which can lead to cognitive enhancement in healthy people and better rehabilitation in patients. The increased use of EEG neurofeedback highlights the urgent need to reduce the discomfort and preparation time and increase the stability and simplicity of the system’s operation. Based on brain-computer interface technology and a multithreading design, we describe a neurofeedback system with an integrated design that incorporates wearable, multichannel, dry electrode EEG acquisition equipment and cognitive function assessment. Then, we evaluated the effectiveness of the system in a single-blind control experiment in healthy people, who increased the alpha frequency band power in a neurofeedback protocol. We found that upregulation of the alpha power density improved working memory following short-term training (only five training sessions in a week), while the attention network regulation may be related to other frequency band activities, such as theta and beta. Our integrated system will be an effective neurofeedback training and cognitive function assessment system for personal and clinical use.

On the cyclic nature of perception in vision versus audition

Does our perceptual awareness consist of a continuous stream, or a discrete sequence of perceptual cycles, possibly associated with the rhythmic structure of brain activity? This has been a long-standing question in neuroscience. We review recent psychophysical and electrophysiological studies indicating that part of our visual awareness proceeds in approximately 7-13 Hz cycles rather than continuously. On the other hand, experimental attempts at applying similar tools to demonstrate the discreteness of auditory awareness have been largely unsuccessful. We argue and demonstrate experimentally that visual and auditory perception are not equally affected by temporal subsampling of their respective input streams: video sequences remain intelligible at sampling rates of two to three frames per second, whereas audio inputs lose their fine temporal structure, and thus all significance, below 20-30 samples per second. This does not mean, however, that our auditory perception must proceed continuously. Instead, we propose that audition could still involve perceptual cycles, but the periodic sampling should happen only after the stage of auditory feature extraction. In addition, although visual perceptual cycles can follow one another at a spontaneous pace largely independent of the visual input, auditory cycles may need to sample the input stream more flexibly, by adapting to the temporal structure of the auditory inputs.

Oscillatory Brain Correlates of Live Joint Attention: A Dual-EEG Study

Joint attention consists in following another's gaze onto an environmental object, which leads to the alignment of both subjects' attention onto this object. It is a fundamental mechanism of non-verbal communication, and it is essential for dynamic, online, interindividual synchronization during interactions. Here we aimed at investigating the oscillatory brain correlates of joint attention in a face-to-face paradigm where dyads of participants dynamically oriented their attention toward the same or different objects during joint and no-joint attention periods respectively. We also manipulated task instruction: in socially driven instructions, the participants had to follow explicitly their partner's gaze, while in color-driven instructions, the objects to be looked at were designated at by their color so that no explicit gaze following was required. We focused on oscillatory activities in the 10 Hz frequency range, where parieto-occipital alpha and the centro-parietal mu rhythms have been described, as these rhythms have been associated with attention and social coordination processes respectively. We tested the hypothesis of a modulation of these oscillatory activities by joint attention. We used dual-EEG to record simultaneously the brain activities of the participant dyads during our live, face-to-face joint attention paradigm. We showed that joint attention periods - as compared to the no-joint attention periods - were associated with a decrease of signal power between 11 and 13 Hz over a large set of left centro-parieto-occipital electrodes, encompassing the scalp regions where alpha and mu rhythms have been described. This 11-13 Hz signal power decrease was observed independently of the task instruction: it was similar when joint versus no-joint attention situations were socially driven and when they were color-driven. These results are interpreted in terms of the processes of attention mirroring, social coordination, and mutual attentiveness associated with joint attention state.

Three methods compared for detecting the onset of alpha wave synchronization following eye closure

Recent work indicates that the variation in the occipital alpha wave component of the EEG spectrum, controlled through eye closure, can be used by an untrained person to effect reliable activation of electrical devices. Here we describe and compare three real-time strategies, based on analogue and digital signal processing methods, of detecting the onset of alpha wave synchronization during eye closure. The goal of this work is to establish a method which satisfies the condition of rapid detection of alpha wave enhancement, thereby allowing for the efficient activation of devices, while simultaneously registering few or no false positives due to the natural variation in the alpha signal with eyes open. This work, based on measurements on 15 subjects in the age range 12 to 40 years, indicates that renal-time analysis of the EEG power spectrum provides for rapid detection of the onset of alpha wave synchronization while maintaining low counts of false positives.

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.

Effects of illumination on the rabbit's EEG during the two phases of its circadian rhythm

After exposure to a LD 12:12 regimen for several weeks, rabbits exhibit a programmed circadian rhythm in the RMS values of their occipital and frontal EEG's during 54-hr recordings in constant darkness. Illumination at levels of 80, 160 and 230 Lx raises these RMS values in both phases of the rhythm. The induced rise is large in the phase with low RMS values and small in the other, whereas light-induced changes in spectral composition of the EEG's are slight in either phase. Bilateral optic nerve sectioning results in similar changes in properties of the EEG and in the amplitude of its rhythm. The results are discussed with reference to the influence exerted by steady illumination on the overall-level of retinal maintained "dark" discharge.

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.

Individual differences in alpha rhythm responsivity: inter-task consistency and relationships to cardiovascular and dispositional variables

Individual differences in EEG alpha rhythm responsivity were examined with respect to: (1) consistency of response across cognitive tasks; (2) relationships to cardiovascular responsivity; and (3) relationships to dispositional variables. Inter-task correlations revealed a significant degree of stability in subjects' alpha responses to four "sensory rejection" tasks: mental arithmetic, time estimation and imagining oneself as cold or warm. Individuals evidencing greater suppression of alpha activity during mental arithmetic also displayed greater heart rate increase and greater digital vasoconstriction, as well as obtaining higher scores on the Activity subscale of the EASI-III Temperament Survey and on the "Hard Striving" subscale of the Jenkins Activity Survey for Health Prediction, a measure of the Coronary-Prone Behavior Pattern. Alpha responsivity in the time estimation and warm imagery tasks was also associated with greater heart rate increase. The results suggest that alpha responsivity is related to individual differences affecting one's attentiveness or involvement in experimental tasks.

Ocular-motor effects on the human electroencephalogram

In response to the findings that gross vertical and horizontal eye deviation can be associated with facilitation of the human EEG alpha rhythm, an hypothesis is suggested that the deviation of gaze which exceeds a critical angle and results in a loss of subjective ocular stability is related to the occurrence of the paradoxical alpha effect.

Alpha and kappa electroencephalogram activity in eyeless subjects

Several reports have cast doubt on the cerebral origin of alpha and kappa electroencephalogram activity by charging that they are artifacts related to eye activity. Data are cited which eliminate the corneoretinal potential of the eyeball, tremor of the extraocular muscles, eye position, accommodation, and eye flutter as sources of alpha and kappa electroencephalogram activity. A subject with both eyes removed showed normal alpha and kappa electroencephalogram activity. Marked left-right differences in alpha activity were not found in one-eyed subjects whose eyes and extraocular muscles were completely removed on one side.