Neuronal oscillations in the EEG under varying cognitive load: A comparative study between slow waves and faster oscillations

ObjectiveThis study has been specifically designed to investigate very low frequency neuronal oscillations (VLFO, <0.5 Hz) during resting states and during goal-directed tasks of graded difficulty levels, quantify the changes that the slow waves undergo in these conditions and compare them with those for higher frequency bands (namely delta, theta and alpha).MethodsTo this end we developed a multistage signal processing methodology comprising blind source separation coupled with a neural network based feature extraction and classification method.ResultsChanges in the amplitude and phase of brain sources estimates in the VLF band between rest and task were enhanced with increased task difficulty, but remained lower than those experienced in higher frequency bands. The slow wave variations were also significantly correlated with task performance measures, and hence with the level of task-directed attention.ConclusionsThese findings suggest that besides their prominent sensitivity to external stimulation, VLFOs also contribute to the cortical ongoing background activity which may not be specifically related to task-specific attention and performance.SignificanceOur work provides important insight into the association between VLF brain activity and conventional EEG frequency bands, and presents a novel framework for assessing neural activity during various mental conditions and psychiatric states.

► We present a novel approach for exploring the functional relationship between very low frequency EEG oscillations (VLFO, <0.5 Hz) recorded at rest and those following the transition to goal-directed tasks of different difficulty levels.
► We show that VLFOs are sensitive to variations in cognitive load, and are attenuated but not extinguished following a rest-to-task transition.
► We present a new signal processing methodology for quantifying changes in band-limited EEG activity, which can be used to investigate altered functioning of brain oscillators in psychiatric and neurobehavioural disorders.