Consistency Conditions in Synchronization

Abstract

Objective

We examined consistency conditions in synchronization (event-related desynchronization/synchronization; ERD/ERS) that have been linked to individual differences in cognitive ability demonstrate satisfying temporal stability and cross-situational consistency.

Methods

Multi-channel EEG recordings from 29 adults, assessed at three different occasions over 2 years were examined. Between-session correlations and consistency coefficients (Cronbach's alpha) across the three experiments were evaluated for both, spectral power features of the resting EEG and ERD/ERS estimates while the participants performed some cognitive task (i.e. different elementary cognitive tasks that put comparable demands on the participants).

Results

ERD/ERS values, while subjects performed a cognitive task, demonstrated satisfactory stability and consistency (i.e. >0.7), whereby the degree of consistency varied as a function of frequency band and brain region. Highest consistency was found for the 8-10 Hz ERD in parieto-occipital recording sites (i.e. >0.9). In resting EEG, mean alpha (gravity) frequency was the most stable EEG feature.

Conclusions

The present data suggest that ERD/ERS phenomena in different narrow frequency bands are rather stable over time and across different situations. The relatively high reproducibility of ERD/ERS promotes the usefulness of this measure in assessing individual differences of physiological activation patterns accompanying cognitive performance.

Significance

This study addresses the issue of reproducibility of EEG in general and ERD/ERS experiments in particular, which is a prerequisite for both basic research and clinical studies.

Consistency Conditions in Synchronization

1. Introduction

One possibility for assessing the functional state of the brain (i.e. cortical activation/deactivation) is the study of frequency-specific amplitude changes of the ongoing EEG. Stimulus- or task-related changes in different EEG frequency bands can be measured, for example, by the quantification of Event-Related (De-)synchronization (ERD/ERS; originally described by Pfurtscheller and Aranibar, 1977; for a comprehensive review see Pfurtscheller and Lopes da Silva, 1999). ERD is defined as an amplitude or power decrease compared with a resting state, whereas ERS denotes an increase in amplitude or power of a defined frequency band. In the alpha band, ERD (i.e. a decrease in alpha power) is most probably associated with an activation of the respective cortical areas involved in processing of sensory or cognitive information. Alpha band ERS, on the contrary, has been assumed to reflect an idling state of the brain or even a kind of deactivation of cortical areas (Neuper and Pfurtscheller, 2001 and Pfurtscheller, 1992).

ERD/ERS in the alpha band has been widely used to study changes in cortical activation as a function of both task-related aspects and more permanent factors, such as individual differences in cognitive performance. On the one hand, associations between cognitive load and alpha band desynchronization have been reported (e.g. Boiten et al., 1992, Dujardin et al., 1995, Dujardin et al., 1999, Klimesch et al., 1993, Stipacek et al., 2003 and Van Winsum et al., 1984). These studies typically demonstrate that with increasing processing resources required by a task the alpha power decreases, particularly in the upper alpha band (Stipacek et al., 2003). On the other hand, ERD in the alpha band has also been examined for its discriminative value in cognitive abilities and other psychometric and clinical variables. It has been ...