EEG correlates of cognitive load in a multiple choice reaction task.

The present study aimed to examine EEG correlates of cognitive load in a task, in which multiple stimulus‑response mappings have to be maintained in working memory (WM) combined with selective inhibition of irrelevant stimulus‑response mappings on every trial. Twenty‑four healthy younger adults had to perform choice reaction tasks differed in the number of S‑R mappings and motor response requirements. Performance was lower in the high load than in the low load condition. Performance decline at higher WM loads was accompanied by an increase of EEG power in delta, theta, and beta frequency bands and by a reduction in alpha band. The effect on alpha was generalized across all the electrodes. Correlations between EEG and performance were observed in the high load condition but not in the low load condition. Theta activity negatively correlated with reaction time, whereas positive correlations between beta activity and reaction time were found. The two frequency bands negatively correlated with each other at all electrodes. The results suggest that changes in alpha and theta power may be considered as the most sensitive indicators of cognitive load. The alpha reduction may be related to activation of widespread cortical areas which were recruited for performance of complex WM tasks. The beta increase, especially in the beta‑2 range, may partly be associated with activation of motor cortex due to difficulties in preparation and execution of motor responses. Theta increases may be considered as an index of facilitation of information processing in WM and improvements in higher‑order executive control, which in turn facilitates motor processes.