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Cognitive control: novel brain mechanisms revealed by time-frequence analysis of the electroencephalogram under experimental tasks involving high attentional load
Cognitive control includes maintenance of task-specific processes related to attention, and non-specific regulation of motor threshold. Generally, two different kinds of errors may occur, with some errors related to attentional lapses and decision uncertainty, and some errors – to failures of sustaining motor threshold. Error commission leads to adaptive adjustments in brain networks that subserve goal-directed behavior, resulting in either enhanced stimulus processing or increased motor threshold depending on the nature of errors committed. We report here two studies using the auditory version of the two-choice condensation task, which is highly demanding for sustained attention while involves no inhibition of prepotent responses. We analyzed power and topography of EEG oscillations in theta, alpha, and beta frequency bands.
Experiment 1. We studied post-error adaptive adjustments resulting in optimized brain processing and behaviour on subsequent trials. Errors were followed by increased frontal midline theta (FMT) activity, as well as by enhanced alpha band suppression in the parietal and the left central regions; parietal alpha suppression correlated with the task performance, left central alpha suppression correlated with the post-error slowing, and FMT increase correlated with both behavioral measures. On post-error correct trials, left-central alpha band suppression started earlier before the response, and the response was followed by weaker FMT activity, as well as by enhanced alpha band suppression distributed over the entire scalp. These findings show the existence of three separate neuronal networks involved in post-error adjustments: the midfrontal performance monitoring network, the parietal attentional network, and the sensorimotor network.
Experiment 2. We studied if response time may be a valid approximation distinguishing trials with high and low levels of sustained attention and decision uncertainty. We found that error-related FMT activity was present only on fast erroneous trials. The feedback-related FMT activity was equally strong on slow erroneous and fast erroneous trials. Late post-response posterior alpha suppression was stronger on erroneous slow trials. Feedbackrelated frontal beta oscillations were present only on slow correct trials. The data obtained cumulatively suggests that response time allows distinguishing the two types of trials, with fast trials related to higher levels of attention and low uncertainty, and slow trials related to lower levels of attention and higher uncertainty.