Understanding and enhancing locomotor adaptation using transcranial stimulation

Human locomotor adaptation is necessary to maintain flexibility of walking. Adaptation has also been demonstrated to have considerable rehabilitative potential. In this dissertation we used transcranial stimulation to assess changes in neural excitability following locomotor adaptation. We then used this information to target important neural areas with direct current stimulation to facilitate adaptation in healthy individuals and individuals with gait impairments from cerebral damage.;Human locomotor adaptive learning is thought to involve the cerebellum, but the neurophysiological mechanisms underlying this process are not known. While animal research has pointed to depressive modulation of cerebellar outputs, a direct correlation between adaptive learning and cerebellar depression has never been demonstrated. First we used transcranial magnetic stimulation to assess excitability changes occurring in the cerebellum and primary motor cortex (M l) after individuals learned a new locomotor pattern on the split-belt treadmill. To control for potential changes associated to task performance complexity, the same group of subjects was also assessed after performing 2 other locomotor tasks that did not elicit learning. We found that only adaptive learning resulted in reduction of cerebellar inhibition, and that this reduction was correlated with the magnitude of learning. This finding suggests that the cerebellum might be a valuable target to enhance with non-invasive brain stimulation to enhance motor learning.;In our second study, we examined whether transcranial direct current stimulation (tDCS) over the cerebellum could in fact enhance locomotor adaptation in healthy individuals. We found that anodal cerebellar tDCS applied during adaptation expedited the adaptive process while cathodal cerebellar tDCS slowed it down, without affecting the rate of de-adaptation. Interestingly cerebellar tDCS affected the adaptation rate of spatial but not temporal elements of walking. In our third study, we investigated the effects of non-invasive stimulation of the spinal cord to enhance locomotor adaptation. We found that anodal spinal stimulation during adaptation facilitated learning in the temporal domain but not in the spatial domain. These two studies allowed us to double dissociate the role of the cerebellum and spinal circuitry in locomotor adaptation. Our results suggest that tDCS could be used as a tool to modulate locomotor training in neurological patients with gait impairments.;In our final study, we investigated the effects of cerebellar tDCS on split-belt locomotor adaptation in a group of chronic stroke patients. We have previously shown that gait symmetry can be induced in stroke patients using our locomotor adaptation task and we wondered whether tDCS would facilitate this effect. We discovered that anodal tDCS affected adaptation in patients by reducing the amount forgotten during each 5- minute break relative sham. Interestingly, in the patient group only, anodal tDCS also slowed the rate of de-adaptation, increasing the duration patients walking with more symmetric steps. This study provides evidence of how cerebellar tDCS can selectively enhance motor adaptation in individuals with stroke and bring up the possibility that we may be able to use tDCS as a tool in rehabilitation to extend the effects of adaptation training.