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Stimuli may induce only partial consciousness-an intermediate between null and full consciousness-where the presence but not identity of an object can be reported. The differences in the neuronal basis of full and partial consciousness are poorly understood. We investigated if evoked and oscillatory activity could dissociate full from partial conscious perception. We recorded human cortical activity with magnetoencephalography (MEG) during a visual perception task in which stimulus could be either partially or fully perceived. Partial consciousness was associated with an early increase in evoked activity and theta/low-alpha-band oscillations while full consciousness was also associated with late evoked activity and beta-band oscillations. Full from partial consciousness was dissociated by stronger evoked activity and late increase in theta oscillations that were localized to higher-order visual regions and posterior parietal and prefrontal cortices. Our results reveal both evoked activity and theta oscillations dissociate partial and full consciousness., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Preterm birth is the greatest risk factor for lifelong neurocognitive deficits, globally. The effect of prematurity on early cortical network function has, however, remained poorly understood. Here, we developed a novel methodology that allows reliable assessment of functional connectivity in neonatal brain activity at millisecond and multisecond scales in terms of cortical phase and amplitude correlations, respectively. We measured scalp electroencephalography at term-equivalent age in infants exposed to very early prematurity as well as in healthy controls. We found that newborn cortical activity organizes into multiplex networks that differ significantly between vigilance states. As compared with healthy control infants, prematurity was found to cause frequency-specific patterns of dysconnectivity in cortical network, changes that were distinct for networks of phase and amplitude correlations. Neuroanatomically, the most prominent markers of prematurity were found in connections involving the frontal regions. Phase synchrony in frontally connected networks was correlated with newborn neurological performance, suggesting the first measure of cortical functional coupling that correlates with neurological performance in human infant.

Visuospatial attention prioritizes processing of attended visual stimuli. It is characterized by lateralized alpha-band (8-14 Hz) amplitude suppression in visual cortex and increased neuronal activity in a network of frontal and parietal areas. It has remained unknown what mechanisms coordinate neuronal processing among frontoparietal network and visual cortices and implement the attention-related modulations of alpha-band amplitudes and behavior. We investigated whether large-scale network synchronization could be such a mechanism. We recorded human cortical activity with magnetoencephalography (MEG) during a visuospatial attention task. We then identified the frequencies and anatomical networks of inter-areal phase synchronization from source localized MEG data. We found that visuospatial attention is associated with robust and sustained long-range synchronization of cortical oscillations exclusively in the high-alpha (10-14 Hz) frequency band. This synchronization connected frontal, parietal and visual regions and was observed concurrently with amplitude suppression of low-alpha (6-9 Hz) band oscillations in visual cortex. Furthermore, stronger high-alpha phase synchronization was associated with decreased reaction times to attended stimuli and larger suppression of alpha-band amplitudes. These results thus show that high-alpha band phase synchronization is functionally significant and could coordinate the neuronal communication underlying the implementation of visuospatial attention., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Neuronal activity in sensory and fronto-parietal (FP) areas underlies the representation and attentional control, respectively, of sensory information maintained in visual working memory (VWM). Within these regions, beta/gamma phase-synchronization supports the integration of sensory functions, while synchronization in theta/alpha bands supports the regulation of attentional functions. A key challenge is to understand which mechanisms integrate neuronal processing across these distinct frequencies and thereby the sensory and attentional functions. We investigated whether such integration could be achieved by cross-frequency phase synchrony (CFS). Using concurrent magneto- and electroencephalography, we found that CFS was load-dependently enhanced between theta and alpha-gamma and between alpha and beta-gamma oscillations during VWM maintenance among visual, FP, and dorsal attention (DA) systems. CFS also connected the hubs of within-frequency-synchronized networks and its strength predicted individual VWM capacity. We propose that CFS integrates processing among synchronized neuronal networks from theta to gamma frequencies to link sensory and attentional functions., Competing Interests: The authors declare that no competing interests exist.

Objective: To assess how the recording montage in the neonatal EEG influences the detection of cortical source signals and their phase interactions., Methods: Scalp EEG was simulated by forward modeling 20-200 simultaneously active sources covering the cortical surface of a realistic neonatal head model. We assessed systematically how the number of scalp electrodes (11-85), analysis montage, or the size of cortical sources affect the detection of cortical phase synchrony. Statistical metrics were developed for quantifying the resolution and reliability of the montages., Results: The findings converge to show that an increase in the number of recording electrodes leads to a systematic improvement in the detection of true cortical phase synchrony. While there is always a ceiling effect with respect to discernible cortical details, we show that the average and Laplacian montages exhibit superior specificity and sensitivity as compared to other conventional montages., Conclusions: Reliability in assessing true neonatal cortical synchrony is directly related to the choice of EEG recording and analysis configurations. Because of the high conductivity of the neonatal skull, the conventional neonatal EEG recordings are spatially far too sparse for pertinent studies, and this loss of information cannot be recovered by re-montaging during analysis., Significance: Future neonatal EEG studies will need prospective planning of recording configuration to allow analysis of spatial details required by each study question. Our findings also advice about the level of details in brain synchrony that can be studied with existing datasets or by using conventional EEG recordings., (Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Visual working memory (VWM) sustains information online as integrated object representations. Neuronal mechanisms supporting the maintenance of feature-specific information have remained unidentified. Synchronized oscillations in the gamma band (30-120 Hz) characterize VWM retention and predict task performance, but whether these oscillations are specific to memorized features and VWM contents or underlie general executive VWM functions is not known. In the present study, we investigated whether gamma oscillations reflect the maintenance of feature-specific information in VWM. Concurrent magneto- and electroencephalography was recorded while subjects memorized different object features or feature conjunctions in identical VWM experiments. Using a data-driven source analysis approach, we show that the strength, load-dependence, and source topographies of gamma oscillations in the visual cortex differentiate these memorized features. Load-dependence of gamma oscillations in feature-specific visual and prefrontal areas also predicts VWM accuracy. Furthermore, corroborating the hypothesis that gamma oscillations support the perceptual binding of feature-specific neuronal assemblies, we also show that VWM for color-location conjunctions is associated with stronger gamma oscillations than that for these features separately. Gamma oscillations hence support the maintenance of feature-specific information and reflect VWM contents. The results also suggest that gamma oscillations contribute to feature binding in the formation of memory representations., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

During non-rapid eye movement (NREM) sleep (stage N3), when consciousness fades, cortico-cortical interactions are impaired while neurons are still active and reactive. Why is this? We compared cortico-cortical evoked-potentials recorded during wakefulness and NREM by means of time-frequency analysis and phase-locking measures in 8 epileptic patients undergoing intra-cerebral stimulations/recordings for clinical evaluation. We observed that, while during wakefulness electrical stimulation triggers a chain of deterministic phase-locked activations in its cortical targets, during NREM the same input induces a slow wave associated with an OFF-period (suppression of power>20Hz), possibly reflecting a neuronal down-state. Crucially, after the OFF-period, cortical activity resumes to wakefulness-like levels, but the deterministic effects of the initial input are lost, as indicated by a sharp drop of phase-locked activity. These findings suggest that the intrinsic tendency of cortical neurons to fall into a down-state after a transient activation (i.e. bistability) prevents the emergence of stable patterns of causal interactions among cortical areas during NREM. Besides sleep, the same basic neurophysiological dynamics may play a role in pathological conditions in which thalamo-cortical information integration and consciousness are impaired in spite of preserved neuronal activity., (Copyright © 2015. Published by Elsevier Inc.)

Background: Source-reconstructed magneto- and electroencephalography (M/EEG) are promising tools for investigating the human functional connectome. To reduce data, decrease noise, and obtain results directly comparable to magnetic resonance imaging (MRI), M/EEG source data can be collapsed into a cortical parcellation. For most collapsing approaches, however, it remains unclear if collapsed parcel time series accurately represent the coherent source dynamics within each parcel., New Method: We introduce a collapse-weighting-operator optimization approach that maximizes parcel fidelity, i.e., the phase correlation between original source dynamics and collapsed parcel time series, and thereby the accuracy with which the source dynamics are retained in forward and inverse modeling., Results: The sparse, optimized weighting operator increased parcel fidelity 57-73% and true positive rate of interaction mapping from 0.33 to 0.84 in comparison to a non-sparse weighting approach. These improvements were robust for variable source topographies and parcellation resolutions. Critically, in real inverse-modeled MEG data, the optimized operator yielded close-to-perfect intra-parcel coherence., Comparison With Existing Methods: Previous suggestions for obtaining parcel time series include averaging all source time series within each anatomical parcel or using exclusively the time series of the voxel with maximum power. These methods are sensitive to signal heterogeneity and outlier sources. The approach advanced here avoids these problems., Conclusions: The optimized operator is suitable for collapsing real source-reconstructed M/EEG data into any cortical parcellation. The enhanced time series reconstruction fidelity yields improved accuracy of subsequent analyses of both local dynamics and large-scale interaction mapping., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Several studies show that the amplitudes of human brain oscillations are modulated during the performance of visual working memory (VWM) tasks in a load-dependent manner. Less is known about the dynamics and identities of the cortical regions in which these modulations take place, and hence their functional significance has remained unclear. We used magnetoencephalography and electroencephalography together with minimum norm estimate-based source modeling to study the dynamics of ongoing brain activity during a parametric VWM task. Early stimulus processing and memory encoding were associated with a memory load-dependent spread of neuronal activity from occipital to temporal, parietal, and frontal cortical regions. During the VWM retention period, the amplitudes of oscillations in theta/alpha- (5-9 Hz), high-alpha- (10-14 Hz), beta- (15-30 Hz), gamma- (30-50 Hz), and high-gamma- (50-150 Hz) frequency bands were suppressed below baseline levels, and yet, in frontoparietal regions, load dependently strengthened. However, in occipital and occipitotemporal structures, only beta, gamma, and high-gamma amplitudes were robustly strengthened by memory load. Individual behavioral VWM capacity was predicted by both the magnitude of the N1 evoked response component in early visual regions and by the amplitudes of frontoparietal high-alpha and high-gamma band oscillations. Thus, both early stimulus processing and late retention period activities may influence the behavioral outcome in VWM tasks. These data support the notion that beta- and gamma-band oscillations support the maintenance of object representations in VWM whereas alpha-, beta-, and gamma-band oscillations together contribute to attentional and executive processing.

The amplitude of alpha-frequency band (8-14 Hz) activity in the human electroencephalogram is suppressed by eye opening, visual stimuli and visual scanning, whereas it is enhanced during internal tasks, such as mental calculation and working memory. alpha-Frequency band oscillations have hence been thought to reflect idling or inhibition of task-irrelevant cortical areas. However, recent data on alpha-amplitude and, in particular, alpha-phase dynamics posit a direct and active role for alpha-frequency band rhythmicity in the mechanisms of attention and consciousness. We propose that simultaneous alpha-, beta- (14-30 Hz) and gamma- (30-70 Hz) frequency band oscillations are required for unified cognitive operations, and hypothesize that cross-frequency phase synchrony between alpha, beta and gamma oscillations coordinates the selection and maintenance of neuronal object representations during working memory, perception and consciousness.

Spontaneous transients of correlated activity are a characteristic feature of immature brain structures, where they are thought to be crucial for the establishment of precise neuronal connectivity. Studies on experimental animals have shown that this kind of early activity in cortical structures is composed of long-lasting, intermittent network events, which undergo a developmental decline that is closely paralleled by the maturation of GABAergic inhibition. In order to examine whether similar events occur in the immature human cortex, we performed direct current-coupled electroencephalography (EEG) recordings from sleeping preterm babies. We show now that much of the preterm EEG activity is confined to spontaneous, slow activity transients. These transients are characterized by a large voltage deflection that nests prominent oscillatory activity in several frequency bands covering the whole frequency spectrum of the preterm EEG (<0.1-30 Hz). The slow voltage deflections had an amplitude of up to 800 microV. Most of these 'giant' events originated in the temporo-occipital areas, with a maximum rate of about 8/min, and their occurrence as well as amplitude showed a decline by the time of normal birth. In age-matched fetal brain tissue, this decrease in the spontaneous activity transients was associated with a developmental up-regulation of the neuronal chloride extruder K+-Cl- cotransporter 2, a crucial molecule for the generation of inhibitory GABAergic Cl- currents. Our work indicates that slow endogenous activity transients in the immature human neocortex are mostly confined to the prenatal stage and appear to be terminated in parallel with the maturation of functional GABAergic inhibition.

Synchronization of neuronal activity, often associated with network oscillations, is thought to provide a means for integrating anatomically distributed processing in the brain. Neuronal processing, however, involves simultaneous oscillations in various frequency bands. The mechanisms involved in the integration of such spectrally distributed processing have remained enigmatic. We demonstrate, using magnetoencephalography, that robust cross-frequency phase synchrony is present in the human cortex among oscillations with frequencies from 3 to 80 Hz. Continuous mental arithmetic tasks demanding the retention and summation of items in the working memory enhanced the cross-frequency phase synchrony among alpha (approximately 10 Hz), beta (approximately 20 Hz), and gamma (approximately 30-40 Hz) oscillations. These tasks also enhanced the "classical" within-frequency synchrony in these frequency bands, but the spatial patterns of alpha, beta, and gamma synchronies were distinct and, furthermore, separate from the patterns of cross-frequency phase synchrony. Interestingly, an increase in task load resulted in an enhancement of phase synchrony that was most prominent between gamma- and alpha-band oscillations. These data indicate that cross-frequency phase synchrony is a salient characteristic of ongoing activity in the human cortex and that it is modulated by cognitive task demands. The enhancement of cross-frequency phase synchrony among functionally and spatially distinct networks during mental arithmetic tasks posits it as a candidate mechanism for the integration of spectrally distributed processing.