Lateralization of posterior-parietal cortex contributions to motor learning

Project Summary: Motor learning is fundamental for humans to become proficient in daily activities, such as self-care, work, and leisure. Two fundamental components of motor learning in humans, motor adaptation and skill learning, are critical for acquiring new activities. For example, when learning a new sport, such as pickleball, one adapts previously learned tennis skills (adaptation) while also learning components unique to the sport at hand (skill learning). This proposal details a set of studies aimed at understanding the functional neuroanatomy of these two learning processes. Converging evidence implicates a major role of posterior parietal cortex (PPC) in visuomotor learning. We have previously shown that left, but not right, posterior parietal lesions in stroke patients prevent motor adaptation with both the contralesional and ipsilesional arms, indicating that learning is lateralized to the left hemisphere. This proposal will utilize two types of non-invasive brain stimulation (NIBS) in humans to ask the following questions: Are there hemisphere-specific effects on the two types of motor learning?, and can learning and/or transfer be facilitated by excitatory stimulation to posterior parietal cortex? We will examine interlimb transfer of learning as a reflection of consolidation of effector-independent motor memories. Our overarching hypothesis is that HD-tDCS delivered exclusively to the left PPC will facilitate learning and/or transfer in each of the adaptation and skill learning tasks, and that this facilitation will be plausibly attributable to motor consolidation between trials. We will test these hypotheses through three aims that address 1) whether anodal high-definition transcranial direct current stimulation (HD-tDCS) delivered to left, but not right, posterior parietal cortex will facilitate visuomotor adaptation and interlimb transfer in both arms, 2) whether anodal HD-tDCS delivered to left, but not right, posterior parietal cortex will facilitate skill learning and interlimb transfer in both arms, and 3) whether double pulse TMS delivered to the left, but not the right, PPC, either prior to movement or during movement, will affect learning and transfer in both tasks. This last aim will help to elucidate the mechanisms underlying posterior parietal cortex mediated learning. Our pilot data strongly support a substantial effect of NIBS to the left PPC on distinct aspects of these two motor learning processes. The information gained from this study should prove essential for the optimal translation of non-invasive brain stimulation techniques to motor learning in rehabilitation. This proposal brings together the complimentary expertise of two research programs: Dr. Sainburg has developed the proposed behavioral paradigms, related software/hardware, and his team has expertise in the neural basis of motor control, learning, and lateralization. Dr. Tunik studies the neural foundations of visual-motor coordination for upper limb movements. His team has specific expertise in the brain stimulation techniques proposed. Both teams have been effectively working together for over a year.