Evolution of cortical activation during recovery from corticospinal tract infarction

Background and Purpose-Recovery from hemiparesis due to corticospinal tract infarction is well documented, but the mechanism of recovery is unknown. F unctional MRI (fMRI) provides a means of identifying focal brain activity r elated to movement of a paretic hand. Although prior studies have suggested that supplementary motor regions in the ipsilesional and contralesional he misphere play a role in recovery, little is known about the time course of cortical activation in these regions as recovery proceeds. Methods-Eight patients with first-ever corticospinal tract lacunes causing hemiparesis had serial fMRIs within the first few days after stroke and at 3 to 6 months. Six healthy subjects were used as controls. Statistically si gnificant voxels during a finger-thumb opposition task were identified with an automated image processing program. An index of ipsilateral versus cont ralateral activity was used to compare relative contributions of the 3,hemi spheres to motor function in the acute and chronic phases after stroke. Results-Controls showed expected activation in the contralateral sensorimot or cortex (SMC), premotor, and supplementary motor areas. Stroke patients d iffered from control patients in showing greater activation in the ipsilate ral SMC, ipsilateral posterior parietal, and bilateral prefrontal regions. Compared with the nonparetic hand, the ratio of contralateral to ipsilatera l SMC activity during movement of the paretic hand increased significantly over time as the paretic hand regained function. Conclusions-The evolution of activation in the SMC from early contralesiona l activity to late ipsilesional activity suggests that a dynamic bihemisphe ric reorganization of motor networks occurs during recovery from hemiparesi s.