Modulation of Cognitive Control Signals in Prefrontal Cortex by Rhythmic Transcranial Magnetic Stimulation

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. By collecting simultaneous electroencephalography (EEG), rhythmic transcranial magnetic stimulation (TMS) has been previously demonstrated to entrain neural oscillations at the frequency of stimulation. Furthermore, when the frequency of entrained neural oscillations is matched to the frequency of endogenous activity in a cognitive task, the brain stimulation improves behavioral performance. Therefore, noninvasive brain stimulation is a promising tool for improving cognition by inducing optimal neural activity via externally applied electromagnetic fields; e.g. cognitive control improvements. Previous evidence has implicated neural activity in the alpha band (8-12 Hz) in information suppression and activity in the theta band (4-7 Hz) in information prioritization. Cognitive control task paradigms have been shown to elicit distinct activity in both of these bands. In this task, the stimuli are lateralized to the right and left visual field during encoding. After a short delay, a cue informs participants which stimuli (right or left) will be tested. Previous evidence found that alpha activity in parietal cortex is generated contralateral to irrelevant stimuli-supporting the role of alpha in information suppression-while theta activity in frontal cortex increases with the number of stimuli to be remembered-supporting the role of theta in information prioritization. For the current study, the investigators propose to deliver rhythmic trains of TMS in either alpha 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. The goal of this experiment is to enhance the observed theta and alpha activity that is seen with the successful prioritization and suppression of information. To provide causal evidence that parietal cortex generates alpha activity and frontal cortex generates theta activity, the investigators will apply rhythmic TMS stimulation to two scalp locations: the anterior middle frontal gyrus and inferior intraparietal sulcus. By applying alpha frequency, theta frequency, and arrhythmic TMS at each location, the investigators will be able to examine the causal relationship of frontal theta oscillations in information prioritization and parietal alpha oscillations in information suppression.