The purpose of this clinical trial is to evaluate the effect of rhythmic transcranial magnetic stimulation (TMS) delivered at delta (2.2 Hz) or theta (6.5 Hz) frequency on cognitive control.

This study aims to explore how targeted stimulation at delta and theta frequencies modulates brain activity to enhance cognitive performance in healthy populations.

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.

Inclusion Criteria:

• Participants must be between the ages of 18 and 35.
• Must be able to provide informed consent.
• Must have normal or corrected-to-normal vision.
• Participants must be right-handed.
• Willingness to comply with all study procedures and availability for the study duration.
• Proficiency in speaking and understanding English.

Exclusion Criteria:

• Must not be color-blind
• Current treatment for ADHD/ADD.
• History of neurological disorders, including but not limited to the following specified conditions
• Epilepsy or seizures (excluding childhood febrile seizures).
• Dementia, Parkinson's disease, multiple sclerosis, cerebral aneurysm, or brain tumors.
• History of stroke or traumatic brain injury.
• Medical conditions or treatments that could interfere with study participation (e.g., unstable cardiac disease, HIV/AIDS, malignancy, or renal impairment).
• Prior brain surgery or presence of brain devices/implants (e.g., cochlear implants or aneurysm clips).
• Females who are pregnant or breastfeeding.
• Use of specific medications, including but not limited to ADHD medications or benzodiazepines, which may interfere with EEG measurements or task performance
• Any condition that, in the opinion of the investigator, increases risk or hinders full compliance with the study.