Involvement of the ipsilateral motor cortex in finger movements of different complexities

TLDR

Functional imaging and behavioral studies indicate that the ipsilateral motor cortex contributes to hand movements, especially for the left hand, and that transient disruption of M1 may differentially affect ipsilateral motor sequences on each side. The study used 15 right‑handed participants who performed simple and complex 8‑second piano sequences while receiving rTMS to the ipsilateral or contralateral primary motor cortex two seconds after sequence onset, with a sham control. Ipsilateral M1 stimulation produced timing errors in both simple and complex sequences, with the complex sequence causing more left‑hand errors than right‑hand errors; left‑hand errors persisted beyond stimulation, indicating that the left hemisphere plays a greater role in timing ipsilateral complex sequences and that ipsilateral M1 contributes to fine finger movements.

Abstract

Abstract Functional imaging and behavioral studies suggest involvement of the ipsilateral hemisphere in hand movements, particularly of the left hand. If this is so, transient disturbance of the motor cortex (M1) with repetitive transcranial magnetic stimulation (rTMS) may affect ipsilateral motor sequences, and the effects may differ on the two sides. We studied 15 right‐handed subjects who played a simple and a complex piano sequence for 8 seconds each. Two seconds after the beginning of each sequence, rTMS was delivered to the ipsilateral or contralateral M1, or directed away from the head (control trial). Ipsilateral M1 stimulation on either side induced timing errors in both sequences, and with the complex sequence induced more timing errors in the left hand than in the right hand. Errors of the right hand with both sequences occurred in the stimulation period only, but errors of the left hand with the complex sequence occurred in both the stimulation and poststimulation periods. We conclude that the ipsilateral M1 is involved in fine finger movements. The left hemisphere plays a greater role in timing ipsilateral complex sequences than the right hemisphere and may be more involved in the processing of complex motor programs.