The role of primary motor cortex (M1) in the control of hand movements is still unclear. FMRI studies of uni-manual performance reported a relationship between level of precision of a motor task and additional ipsilateral M1 (iM1) activation. In the present study we determined whether the demand on accuracy of a movement influences the magnitude of the inhibitory effect between primary motor cortices (IHI). We used transcranial magnetic stimulation (TMS) to measure active IHI (aIHI) of the iM1 on the contralateral M1 (cM1) in the pre-movement period of a left hand task. Ten healthy participants manipulated a joystick to point to targets of two different sizes. For aIHI, the conditioning stimulus (CS) was applied to iM1 and the test stimulus (TS) to cM1 with an interstimulus interval of 10 ms. The amount of the inhibitory effect of the CS on the motor evoked potential (MEP) of the subsequent TS was expressed as percentage of the mean MEP amplitude evoked by the single TS. Across different time points of aIHI measurements in the pre- movement period, there was a significant effect for target size on aIHI. Preparing to point to small targets was associated with weaker aIHI compared to pointing to large targets. The present findings suggest that during the pre- movement period, aIHI from iM1 on cM1 is modulated by the demand on accuracy of the motor task. This is consistent with task fMRI findings showing bilateral M1 activation during high precision movements but only unilateral M1 activity during low precision movements.
- Primary motor cortex
- transcranial magnetic stimulation
- interhemispheric inhibition
- motor control
- Copyright © 2015, Journal of Neurophysiology