| Sensorimotor stroke is the leading cause of permanent disability in United States, often resulting in contralesional hemiparesis characterized by weakness, spasticity, and abnormal synergies in the side contralateral to the damaged hemisphere. Brain damage that results from stroke tends to be predominantly unilateral, due to the hemisphere specificity of cerebral circulation. While a great deal of research has focused on understanding the deficits in the contralateral limbs, very little attention has been given to the fact that the hemispheres are not functionally symmetric for sensorimotor processing. Sainburg et al have previously shown that each hemisphere contributes specific mechanisms to the control of both the arms: the left hemisphere for control of movement trajectory, and the right hemisphere for stabilizing the limb in a steady state position. We propose that each hemisphere imparts its specialized control processes to each arm. A clear prediction of this hypothesis is that damage to the right or left hemisphere due to stroke, should produce hemisphere specific deficits in both the ipsilesional and contralesional arms of stroke patients. In a series of three experiments, we tested whether 1) the contralesional arm motor deficits produced by unilateral stroke patients vary based on the hemisphere of damage and severity of impairment, 2) damage to one hemisphere produces hemisphere-specific motor adaptation deficits in both the arms of the stroke patients and 3) Spontaneous arm selection for reaching tasks are dependent on the hemisphere that is damaged. Our results support our hypothesis that left and right hemisphere damage produces hemisphere-specific deficits in motor control that affect motor adaptation in both the ipsilesional and contralesional arms of stroke patients: While left hemisphere damage produces significantly higher initial direction errors and hand path curvatures (trajectory measures), right hemisphere damage produces significantly higher distance and final position errors during reaching movements. In addition, mild to moderately paretic patients with right hemisphere damage preferred to use their contralesional arm significantly less than the respective arm of their age matched control group. In contrast, mild to moderately paretic patients with left hemisphere damage preferred to use their contralesional right arm to the same extent as the control group's preference to use their right arm. Our findings have significant implications for clinical rehabilitation. |
