The role of the ipsilateral primary motor cortex in movement control after spinal cord injury: a TMS study

Previous neuroimaging studies raised the hypothesis that enhanced activity in the ipsilateral motor cortex (M1) plays a contributing role in the compensation for the motor deficits resulting from a spinal cord injury (SCI). However, it is still unknown whether the activity in the ipsilateral M1 directly contributes to movement performance after SCI. To address this question, we evaluated in five subjects with chronic incomplete cervical SCI the effects of suprathreshold transcranial magnetic stimulation (TMS) to both hemispheres when a movement of the right and left hand was performed separately in the setting of a simple reaction time. We found that stimulation of each hemisphere resulted in delayed simple reaction times in the contralateral but not in the ipsilateral hand. These observations provide the first direct evidence in humans that the ipsilateral M1 did not contribute significantly to motor task performance after SCI.