Modulation of EEG Theta and Alpha Power by an Internal Attention Task with and Without Visual Distractors

Attention to internal representations is crucial in tasks involving temporary storage and mental manipulation of information (working memory tasks), to suppress concurrent interfering processes, such as sensory-intake processes. Theta activity (4–8 Hz), especially frontal, has been extensively associated to working memory tasks, increasing with task complexity and error monitoring. Alpha rhythm (8–14 Hz) has been hypothesized to enhance processes within the attentional focus via inhibition of task-irrelevant regions (alpha increase) and engagement of task-relevant regions (alpha decrease). Here, we provide further contribution to the investigation of alpha and theta activity by computing electroencephalographic (EEG) alpha and theta power from 10 participants who performed a resting phase (no attention) and a mental arithmetic task (internal attention), under two different visual conditions i.e., pictures and no picture presentation. Pictures stimulated external attention and acted as distractors during the math task but not during rest. Results show that frontal theta power increased during the math task vs rest, more largely in presence of visual distractors. Posterior alpha power increased in the math task vs rest in picture condition, but not in the no picture condition; moreover, it decreased in the picture vs no picture condition during rest but not during the math task. These results support frontal theta as a mechanism implementing cortical control in complex tasks and indicate that EEG alpha power reflects a sophisticate balance between increase in some regions and decrease in other regions, depending on the current goal and external context.