The high dimensionality of the human motor system is at the core of the longstanding debate on how the central nervous system controls and learns new movements. Such high dimensionality implies redundancy, i.e., the fact that many combinations of muscle activations can generate the same movement. These muscular patterns lie in the muscular null space, whose exploration plays an important role in the learning of new movements. However, null space activations could be modulated independently from movement-generating activations and used to control external devices for augmentation. Monitoring the changes in neural activations related to such control, for which techniques such as functional near-infrared spectroscopy (fNIRS) can be particularly suited due to their easy applications in complex motor tasks, could lead to new insights on the processes underlying motor learning and motor recovery after neurological lesions. This thesis aims at investigating the effects of exploration and modulation of muscular null space activations. In addition, it tests fNIRS efficacy in the monitoring of brain activations during the execution of a motor task during multiple sessions. Three studies are presented: the adaptation to novel perturbations, that can be compatible or incompatible with the existing muscle synergies of an individual, in a virtual environment across multiple experimental sessions; the simultaneous control of natural motion degrees of freedom and an additional degree of freedom controlled by modulating activations in the muscular null space; and finally, the monitoring of cerebral activity in patients affected by Parkinson’s disease while performing a finger tapping session before and after a thalamotomy performed through magnetic resonance guided focalised ultrasound surgery (MRgFUS). In the first study, participants could not compensate the incompatible perturbations (which requires learning of new synergies and exploration of null space) in the first experimental session, but they were able to reach high level of performance in the last session. These results indicate that, with enough practice, it is possible to learn new null space patterns. The findings of the second study demonstrated that participants were able to modulate null space patterns to successfully control one additional degree of freedom simultaneously with natural ones, although high variability in performance was present among them. Finally, the results of the third study showed that patients’ conditions improved after the MRgFUS treatment, with a consequent change in brain activations highlighted through fNIRS, in agreement with the results obtained in literature using other techniques. The findings of this thesis advance our knowledge on human motor learning mechanisms, and may lead to novel applications, such as personalized neuro-rehabilitation procedures and efficient augmenting devices.
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