The ipsilateral cortico-spinal tract is activated after hemiparetic stroke

The presence of a projection from the primary motor cortex to the ipsilateral muscles has been established in human, but whether this pathway contributes to functional recovery after stroke is unclear. We investigated whether the ipsilateral tract is activated in hemiparetic stroke.

Motor-evoked potentials (MEPs) were simultaneously recorded from the bilateral trapezius or abductor digiti minimi (ADM) muscles after magnetic stimulation to the motor cortex in 40 acute stroke patients.

At rest, ipsilateral trapezius MEPs were recordable in none of the 24 normal controls, and in 38% of the patients after stimulation to the non-affected hemisphere (P < 0.001). With voluntary contraction, ipsilateral trapezius MEPs were elicited in 21% of the normal controls and 73% of the patients (P < 0.001). Ipsilateral ADM MEPs were rarely recordable in both controls (0%) and patients (3%). The presence of ipsilateral trapezius MEPs was associated with less severe paresis in the trapezius (P = 0.04) and deltoid (P = 0.07), but not in the more distal muscles.

The ipsilateral cortico-spinal tract is acutely facilitated after stroke in the trunk or proximal muscles, but not in the hand muscles. Activation of such pathway appears to partly compensate motor dysfunction of the trunk/proximal muscles.