Repetitive stimulation of premotor cortex affects primary motor cortex excitability and movement preparation

BackgroundRepetitive transcranial magnetic stimulation can be used to explore functional connectivity between cortical areas.ObjectiveTo determine the effects of two theta burst stimulation (TBS) patterns (intermittent, iTBS; and continuous, cTBS) of left dorsal premotor cortex (PMd).MethodsLeft PMd was identified in 11 participants using functional magnetic resonance imaging (fMRI), during performance of complex sequential finger movements. Each participant received iTBS, cTBS, or sham TBS of left PMd in three separate sessions within a randomized, single-blind design. The speed and accuracy of simple and complex sequential reaction time (RT) task performance was measured before and after TBS. The excitability of primary motor cortex (M1) bilaterally, and interhemispheric facilitation from left PMd to right M1, were also measured before and after TBS.ResultsiTBS sped up the preparation of complex sequences performed with the right hand, with no detectable changes in M1 excitability. RT performance was maintained after cTBS, in the presence of increased left M1 excitability and suppressed right M1 excitability.ConclusionsFacilitatory and inhibitory TBS protocols applied to left PMd differentially alter corticomotor excitability and behavior, which suggests that these protocols affect different neuronal populations.