Modulation of the Parieto-frontal Communication

Normal Physiology

Paired Associative Stimulation (PAS), Functional Magnetic Resonance Imaging (fMRI), Electrical Field Modeling, Working Memory

Background: Research shows that the parietal and prefrontal areas of the brain are involved in short-term memory. Researchers want to look at the effects of transcranial magnetic stimulation (TMS) of these areas on short-term memory and brain activity. They will use functional magnetic resonance imaging (fMRI) to look at brain activity. Objective: To look at the effects of TMS on brain pathways involved in memory. Eligibility: Healthy, right-handed adults ages 18-50 Design: Participants will have 3 or 4 visits at least 1 week apart. They cannot drink alcohol for at least 48 hours before each visit. The screening visit lasts about 1 (Omega) hours. It can be combined with the first testing visit. Screening includes: * Medical history * Physical exam * Neurological exam * Urine tests * Questionnaires about being left or right handed and about their ability to imagine physical activities. The first testing visit lasts about 1 (Omega) hours and includes an MRI. For the MRI, participants lie on a table that slides into a machine. They will lie still or perform simple memory tasks on a computer screen. The second and third testing visits last about 3 hours. Participants will have: * 2 MRIs * TMS: A wire coil is held to the scalp. A brief electrical current passes through the coil to create a magnetic pulse that affects brain activity. They will perform simple memory tasks. * EMG: Small electrodes are taped to the skin to record muscle activity while they rest. After the study, participants will complete a questionnaire about any discomfort they experienced during the study. ...

Objective: This study aims to identify whether repetitive dual-site transcranial magnetic stimulation (TMS) can modulate the functional connectivity between the parietal and dorso-lateral prefrontal cortices. Study population: The study involves 26 healthy volunteers. Design: This controlled study comprises 3 main visits for each subject: (1) a baseline, evaluation visit during which fMRI will be acquired during a visual short memory task along with diffusion tensor imaging and structural MRI; (2) a visit during which resting state fMRI (rsfMRI) will be acquired, followed by paired-associative stimulation (PAS) with pulses delivered over the parietal and then over the dorso-lateral prefrontal cortex, in order to induce a temporary plastic change in the interaction between the parietal and prefrontal cortices; the PAS will be followed by another rsfMRI and task fMRI; (3) a visit identical to #2 during which the PAS will be delivered with pulses in reverse order of previous visit. Outcome measures: The effects of PAS will be quantified with rsfMRI and a short working memory task, considered as a proxy for complex motor and cognitive control. * The primary outcome will be to investigate the resting state functional connectivity changes induced by each PAS intervention * The secondary outcome #1 will be to evaluate the difference in visual angle error between sessions 2 and 3 in a working memory task during which the subjects will be asked to remember the position of a bar presented on the screen at different time intervals before the inquiry. * The secondary outcome #2 will be to build an fMRI-DTI analysis pipeline for generation of TMS targets individually customized for each subject and a given task.

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