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Student
Title
Supervisor
Faculty
Educational Programme
Final Grade
Year of Graduation
Maria Yurevich
Frequency and State-Dependent Effects of Transcranial Alternating Current Stimulation on Motor Control System
2016
Transcranial alternating current stimulation (tACS) has been shown to affect the ongoing oscillatory activity not only in a frequency-specific, but also in a state-dependent manner.This effect is hypothesized to be caused by entrainment of the cortical oscillations. In a previous study, motor imagery task changed the state of the corticospinal system, and tACS applied over the primary motor cortex (M1) produced facilitation of corticospinal excitability during theta- and, to a lesser extent, alpha-tACS, while at rest motor output increased at beta-tACS.

Here state-and frequency-dependent effects of transcranial alternating current stimulation were further investigated using action observation (thumb-index pinching motion) —— a cognitive task that activates motor cortex and engages mirror neurons system. tACS was delivered at 5, 10, 20, or 40 Hz through electrodes placed over the left M1 (in the hotspot projection of the contralateral first dorsal interosseus (FDI) muscle found using single-pulse transcranial magnetic stimulation) during action and rest observation. Several baseline and sham conditions served as control for the action observation and stimulation effects. Motor evoked potentials (MEPs) induced by applying navigated single-pulse transcranial magnetic stimulation over the electrode allowed to monitor online effects of tACS. MEP amplitudes (peak-to-peak) of the contralateral (right) FDI muscle were measured as indicators of corticospinal excitability.

Maximum corticospinal excitability increase in hand-at-rest observation condition was predictably found during beta-tACS, which is in line with previously obtained data. The most robust corticospinal facilitation during action observation was shown for tACS at alpha frequency.

Taken together, these results confirm state-dependency of tACS effects and provide more detailed view on the mechanisms underlying motor imagery and action observation.

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