Neural Mechanisms Underlying Prism Adaptation

Prism Adaptation (PA) is a non-invasive tool to stimulate short-term visuomotor plasticity that provides the opportunity to experimentally study the consequences of a misalignment of visual and proprioceptive-motor maps and the realignment ability of the human sensori-motor system. In the rehabilitation context it can represent a promising technique to durably ameliorate symptoms of spatial neglect. The present thesis presents five different experiments aimed at clarifying the neural correlates of PA by means of functional brain stimulation. Several PA procedures (Single-step PA, Multiple-Step PA, Reversing PA) and different protocols of transcranial Direct Current Stimulation (tDCS) are combined to assess the role of distinct brain regions (Cerebellum, Posterior Parietal Cortex, Primary Motor Cortex) and their relative connections (Cerebellar-Parietal circuitry) during PA. Results from the present experiments support the theoretical distinction in PA between a strategic mechanism of error correction and a deep process of adaptation. The process of adaptation to prism would be achieved by fast cerebellar involvement during PA, since a very early phase of the pointing performance, and would crucially rely on the connections of this structure with the Parietal Cortex. The continuous information flow between the cerebellum and the PPC would permit full error compensation during PA and cerebellar functioning would allow after-effect development following PA. The after-effect, that can be considered as a kind of motor memory, would be stored in the Primary Motor Cortex and it can be reactivated by means of delayed functional stimulation. The theoretical impact of these findings and possible clinical applications are discussed.