UNDERSTANDING MOTOR LEARNING IMPAIRMENTS DURING VISUOMOTOR ADAPTATION AND INTERLIMB TRANSFER IN PEOPLE WITH MULTIPLE SCLEROSIS

Abstract

Multiple sclerosis (MS) is a chronic neurological disorder characterized by demyelination and neuroaxonal degeneration that can impair motor control and motor learning. Visuomotor adaptation, a type of motor learning, has been widely used to investigate sensorimotor learning capabilities in individuals with various neuromotor impairments, although it has not been studied in people with multiple sclerosis (PwMS). Therefore, I examined the characteristics of visuomotor adaptation, interlimb transfer, and the relative contributions of implicit and explicit learning in this dissertation. Specifically, the purpose of this dissertation was to investigate: (1) visuomotor adaptation with the dominant and nondominant arms in PwMS compared with healthy controls, (2) the pattern of interlimb transfer following visuomotor adaptation in PwMS compared with healthy controls, and (3) the relative contributions of implicit and explicit learning to visuomotor adaptation in PwMS. In Aim I, visuomotor adaptation to a novel visuomotor condition with each arm was examined in 11 PwMS and 20 healthy controls. PwMS demonstrated significantly larger direction errors than controls during the initial stage of adaptation, particularly when adapting with the dominant arm. However, they progressively reduced errors throughout practice and achieved performance comparable to that of healthy controls by the end of adaptation. In contrast, no group differences were observed in terms of final position accuracy. These findings suggest somewhat impaired predictive motor control capabilities but preserved feedback-mediated movement correction abilities in PwMS. In Aim II, the pattern of interlimb transfer following visuomotor adaptation (i.e., adaptation with one arm first, then with the other arm) was examined in the same participants tested in Aim I. Both PwMS and healthy controls demonstrated asymmetrical transfer, with transfer occurring from the nondominant arm to the dominant arm, but not in the opposite direction. Importantly, the overall transfer pattern observed in PwMS was similar to that of healthy controls, indicating that interlimb transfer mechanisms remain largely preserved in PwMS. In Aim III, 20 PwMS adapted to a novel visuomotor condition in one of two experimental conditions: one in which the visuomotor rotation condition was introduced gradually (i.e., implicit learning), and the other in which it was introduced abruptly from the beginning of the adaptation session. Specific information regarding the perturbation was provided to the latter condition (i.e., explicit learning). Participants in the gradual/implicit condition demonstrated greater savings and better retention during readaptation than those in the abrupt/explicit condition. These findings suggest that explicit learning conditions, often considered beneficial for learning in neurotypical individuals, may not have the same positive effects on PwMS. Collectively, this dissertation demonstrates that PwMS exhibit deficits in predictive feedforward motor control while maintaining relatively preserved feedback-mediated control and interlimb transfer mechanisms (aims I and II). Furthermore, it demonstrates that implicit learning conditions lead to more effective learning and more durable motor memory formation than explicit learning in PwMS. These findings advance our understanding of motor learning capabilities in PwMS and provide important implications for the development of rehabilitation interventions that emphasize repetitive practice, error-based sensorimotor learning, and implicit learning strategies in this population.