Effect of coil orientation on motor‐evoked potentials in humans with tetraplegia

Key points Although corticospinal function changes following spinal cord injury (SCI), the extent to which we can activate the corticospinal tract after injury remains poorly understood. To address this question, we used transcranial magnetic stimulation over the hand representation of the primary motor cortex to elicit motor‐evoked potentials (MEPs) using posterior–anterior and anterior–posterior induced currents in the brain and compared them with responses evoked using lateral–medial currents in participants with and without cervical incomplete SCI during small levels of index finger abduction. We found prolonged MEP latencies in all coil orientations in SCI compared to control subjects. However, the latencies of MEPs elicited by posterior–anterior and anterior–posterior compared to lateral–medial stimulation were shorter in SCI compared to controls, particularly for MEPs elicited by anterior–posterior currents. Our findings demonstrate for the first time that corticospinal responses elicited by different directions of the induced current in the brain are differentially affected after SCI.