Abstract
Variation of the magnitude of posterior alpha rhythm (8–12 Hz) has functional and behavioural effects in sensory processing and cognitive performances. Electrical brain activity, as revealed by electroencephalography (EEG), can be represented by a sequence of microstates of about 40–120 ms duration, in which distributed neural pools are synchronously active and generate stable spatial potential topographies on the scalp. Microstate dynamics may reflect transitions between global states characterized by selective inhibition of specific intra-cortical regions, mediated by alpha activity. We investigated the intra-subject and inter-subject relationship between microstate features and alpha band. High-density EEG signals were acquired in 29 healthy subjects during ten minutes of eyes closed rest. Individual EEG signal epochs were classified into four groups depending on the amount of occipital alpha power, and microstate metrics (duration, coverage and frequency of occurrence) were calculated and compared across groups. Correlations between alpha power and microstate metrics between individuals were also performed. To assess if microstate parameter variations are specific for the alpha band, the same analysis was also performed for theta and beta bands, as well as for global field power. We observed an increase in the metrics of microstate, previously associated to the visual system, with the level of intra-subject amplitude alpha oscillations, together with lower coverage of microstate associated with executive attention network and a higher frequency of microstate associated with task negative network. Other modulation effects of broad-band EEG power level on microstate metrics were observed. These effects are not specific for the alpha band, since they can equally be attributed to fluctuations in other frequency bands. We can interpret our results as a regulation mechanism mediated by posterior alpha level, dynamically interacting with other frequency bands, responsible for the switching between active areas.
Highlights
Variation of the magnitude of posterior alpha rhythm (8–12 Hz) has functional and behavioural effects in sensory processing and cognitive performances
Microstate analysis was separately done in 2-second EEG epochs, classified dependently on alpha power amount (L: low, medium-low alpha (ML): medium-low, medium-high alpha (MH): medium-high, H: high, Fig. 1)
Our results showed that, looking at intra-individual alpha variability, the same modulations are observed across different frequency bands for some microstate metrics, but some others seem to change differently with alpha band with respect to other bands
Summary
Variation of the magnitude of posterior alpha rhythm (8–12 Hz) has functional and behavioural effects in sensory processing and cognitive performances. The dynamics of human brain signals uncover organized fluctuations both at rest and during task or sensory input Such time signal variability has been recently linked to the efficiency of functional abilities and directly associated to cognitive performances in functional Magnetic Resonance Imaging (fMRI), Magnetoencephalographic (MEG), Electrocorticographic (ECoG) and Electroencephalographic (EEG) studies (for a review see Buzsáki and colleagues[1]). By looking at EEG www.nature.com/scientificreports recordings at rest, it is evident that different time intervals give rise to a certain degree of alpha variability, even within the state of a closed eyes relaxed vigilance This variability is probably due to different psychological and physiological states at rest during the recording related to alpha-band modulation, possibly originating from the underlying inhibition mechanisms. Coverage is calculated as the percentage of total recording time that a microstate is dominant during a certain condition[18] That is, it indicates the relative presence (i.e. the relative time coverage) of a microstate with respect to the others
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