Exploration of event-induced EEG phase synchronization patterns in cognitive tasks using a time–frequency-topography visualization system

EEG-FCV: An EEG-Based Functional Connectivity Visualization Framework for Cognitive State Evaluation

Electroencephalogram (EEG)-based tools for brain functional connectivity (FC) analysis and visualization play an important role in evaluating brain cognitive function. However, existing similar FC analysis tools are not only visualized in 2 dimensions (2D) but also are highly prone to cause visual clutter and unable to dynamically reflect brain connectivity changes over time. Therefore, we design and implement an EEG-based FC visualization framework in this study, named EEG-FCV, for brain cognitive state evaluation. EEG-FCV is composed of three parts: the Data Processing module, Connectivity Analysis module, and Visualization module. Specially, FC is visualized in 3 dimensions (3D) by introducing three existing metrics: Pearson Correlation Coefficient (PCC), Coherence, and PLV. Furthermore, a novel metric named Comprehensive is proposed to solve the problem of visual clutter. EEG-FCV can also visualize dynamically brain FC changes over time. Experimental results on two available datasets show that EEG-FCV has not only results consistent with existing related studies on brain FC but also can reflect dynamically brain FC changes over time. We believe EEG-FCV could prompt further progress in brain cognitive function evaluation.

Observing baby or sexual videos changes the functional synchronization between the prefrontal and parietal cortices in mothers in different postpartum periods

During the postpartum period (PP), mothers are more sensitive to sensory stimuli related to babies and less sensitive to those with sexual significance. The processing of emotional stimuli requires synchronization among different cerebral areas. This study characterized the cortical electroencephalographic (EEG) correlation in mothers from 1½ to 3 months (PP1), 4 to 5½ months (PP2) and over 6½ months, postpartum (PP3) while observing two videos: one of a baby (BV) and one with sexual content (SV). EEGs were recorded from the frontopolar, dorsolateral and parietal cortices. All three groups rated the BV as pleasant, but only PP3 reported higher sexual arousal with the SV. While watching the BV, PP1 showed a higher correlation among all cortical areas; PP2 manifested a decreased correlation between the prefrontal and parietal cortices, likely associated with the lower emotional modulation of the BV; and PP3 presented a higher synchronization among fewer cortical areas, probably related to longer maternal experience. These cortical synchronization patterns could represent adaptive mechanisms that enable the adequate processing of baby stimuli in new mothers. These data increase our knowledge of the cerebral processes associated with distinct sensitivities to the emotional stimuli that mothers experience during the PP.

Assessment of Multivariate Neural Time Series by Phase Synchrony Clustering in a Time-Frequency-Topography Representation

Most EEG phase synchrony measures are of bivariate nature. Those that are multivariate focus on producing global indices of the synchronization state of the system. Thus, better descriptions of spatial and temporal local interactions are still in demand. A framework for characterization of phase synchrony relationships between multivariate neural time series is presented, applied either in a single epoch or over an intertrial assessment, relying on a proposed clustering algorithm, termed Multivariate Time Series Clustering by Phase Synchrony, which generates fuzzy clusters for each multivalued time sample and thereupon obtains hard clusters according to a circular variance threshold; such cluster modes are then depicted in Time-Frequency-Topography representations of synchrony state beyond mere global indices. EEG signals from P300 Speller sessions of four subjects were analyzed, obtaining useful insights of synchrony patterns related to the ERP and even revealing steady-state artifacts at 7.6 Hz. Further, contrast maps of Levenshtein Distance highlight synchrony differences between ERP and no-ERP epochs, mainly at delta and theta bands. The framework, which is not limited to one synchrony measure, allows observing dynamics of phase changes and interactions among channels and can be applied to analyze other cognitive states rather than ERP versus no ERP.

Significance of Non-phase Locked Oscillatory Brain Activity in Response to Noxious Stimuli

BACKGROUND

Although current pain-evoked electroencephalographic (EEG) studies provide valuable information regarding human brain regions involved in pain, they have mostly considered neuronal responses which oscillate in phase following a painful event. In many instances, cortical neurons respond by generating bursts of activity that are slightly out of phase from trial-to-trial. These types of activity bursts are known as induced brain responses. The significance of induced brain responses to pain is still unknown.

METHODS

In this study, 23 healthy subjects were given both non-painful and painful transcutaneous electrical stimulations in separate testing blocks (stimulation strength was kept constant within blocks). Subjective intensity was rated using a numerical rating scale, while cerebral activity tied to each stimulation was measured using EEG recordings. Induced brain responses were identified using a time frequency wavelet transform applied to average-removed single trials.

RESULTS

Results showed a pain-specific burst of induced theta activity occurring between 180 and 500 ms post-shock onset. Source current density estimations located this activity within the dorsolateral prefrontal cortex (DLPFC, bilaterally), however, only right DLPFC activity predicted a decrease in subjective pain as testing progressed.

CONCLUSION

This finding suggests that non-phase locked neuronal responses in the right DLPFC contribute to the endogenous attenuation of pain through time.

PERSPECTIVE

This article presents neuroimaging findings demonstrating that, in response to pain, non-phase locked bursts of theta activity located in the right dorsolateral prefrontal cortex are associated with a progressive decrease in subjective pain intensity, which has potentially important implications regarding how humans endogenously control their experiences of pain.

Testing for significance of phase synchronisation dynamics in the EEG

A number of tests exist to check for statistical significance of phase synchronisation within the Electroencephalogram (EEG); however, the majority suffer from a lack of generality and applicability. They may also fail to account for temporal dynamics in the phase synchronisation, regarding synchronisation as a constant state instead of a dynamical process. Therefore, a novel test is developed for identifying the statistical significance of phase synchronisation based upon a combination of work characterising temporal dynamics of multivariate time-series and Markov modelling. We show how this method is better able to assess the significance of phase synchronisation than a range of commonly used significance tests. We also show how the method may be applied to identify and classify significantly different phase synchronisation dynamics in both univariate and multivariate datasets.

Prefrontal-parietal correlation during performance of the towers of Hanoi task in male children, adolescents and young adults

Potential age differences in the electroencephalographic (EEG) correlation (r) between the prefrontal and parietal cortices during performance of the Tower of Hanoi task were studied. In three groups of healthy males (G1, 11-13; G2, 18-20, and G3, 26-30, years of age) EEGs were recorded at baseline and during performance of the Tower of Hanoi task. The parameters of the task showed no significant differences among groups, though the majority of younger subjects failed to complete it. The G1 group showed increases only in the interparietal r. The G2 group showed an increased interhemispheric and intrahemispheric r in almost all frequency bands, while the r in G3 increased only in selected frequency bands in the right hemisphere. These findings demonstrate that the functional coupling between these two cortices shows a characteristic pattern during performance of the Hanoi task that, while specific to each age group, was not associated with the successful performance of the task.