Delineating the motor learning network using neuromodulation and effective connectivity

Motor learning is a fundamental aspect of human behavior. A variety of experimental tasks have been used to study motor learning, with most studies focusing either on motor sequence learning (MSL) or visuomotor adaptation (MA). In MSL, a novel pattern of simple movements is learned through repeated practice. In MA, participants learn to adapt their movements to shifted visual feedback. Studies show that in both tasks a cortico-striato-cerebellar network is instrumental for learning. This project aims to characterize connectivity in the cortico-striato-cerebellar network during motor learning using these two well-established paradigms. Connectivity will be studied by interfering with specific network nodes and assessing the effect on behavior and connectivity within the rest of the network. This interference will be established using transcranial application of weak direct currents to the brain. This method, transcranial direct current stimulation (tDCS), has been shown to induce intracerebral current flow and modify spontaneous neuronal excitability by tonic de- or hyperpolarization of resting membrane potentials (Nitsche et al., 2008). TDCS to M1 has been applied in a variety of motor learning tasks and found to have a marked polarity-specific influence on behavior. Recent studies showed that tDCS of the cerebellum has a positive effect on motor learning. Following up on my previous work on causal network interactions in MSL, the current project will first investigate network interactions in the MA variant of motor learning. Second, in order to better understand the role of M1 and cerebellum within the motor learning network, I will stimulate these regions using tDCS and investigate the effects on effective connectivity during MSL and MA using combined tDCS/fMRI study. Together the results of the studies in this project will help to create a well-defined model of motor learning, taking into account different learning modalities (MSL, MA), by determining the critical impact of M1 and cerebellum on effective connectivity and behavior. Clarifying the effect of tDCS on the motor learning network could inform therapeutic interventions in patients with neurodegenerative disorders such as Parkinsons disease and Spino-cerebellar Ataxia, who show specific motor learning deficits.