Causal Role of Delta and Theta Oscillations in Hierarchical Cognitive Control

Neural oscillations are proposed to be a mechanism of coordinating information processing across distributed regions of cortex. Different neural oscillations may correspond to different underlying neural computations. Noninvasive brain stimulation allows experimenters to modulate specific neural oscillations by targeting particular frequency bands. Rhythmic transcranial magnetic stimulation (TMS) has been previously demonstrated to entrain neural oscillations at the frequency of stimulation.

Previous evidence suggests that cognitive control task paradigms elicit distinct activity in both Delta band (2-3 Hz) and Theta band (4-7 Hz). This task is designed to examine hierarchical cognitive control and includes two subtasks. In the Response Task, participants see a colored fixation cross and must make a button press with a specific finger. The stimulus to response mapping is memorized ahead of time. The number of stimulus to response rules is manipulated as four (low set-size) or eight (high set-size). In the Dimension Task, participants see two objects and must judge whether they are the same or different depending on one of two features. One feature is the shape of the object as either tall or wide. The other feature is the complexity of the objects as either being simple and smooth or complex and multifaceted. In this task, delta oscillations (2-3 Hz) are associated with rule abstraction, engaging the mid-dorsolateral prefrontal cortex (mid-dlPFC), while theta oscillations (4-7 Hz) are linked to stimulus-action associations and working memory load, with increased theta activity observed in the dorsal premotor area (PMd) under high set-size conditions.

For the current study, the investigators propose to deliver rhythmic trains of TMS in either delta frequency, theta frequency, or an arrhythmic control to modulate neural processing during a cognitive control task. By collecting simultaneous EEG with TMS, the investigators will be able to measure the entrained oscillations from rhythmic TMS. By applying delta frequency, theta frequency, and arrhythmic TMS during the performance of the task at each location, the investigators will be able to examine the causal relationship of delta oscillations at mid-dlPFC in rule abstraction and theta oscillations at PMd in stimulus-action associations. The stimulation is designed to enhance task performance by amplifying the neural activity patterns observed under these conditions.