Repetitive exposure to prismatic adaptation in post-stroke optic ataxia: a single case study exploring behavioural changes and brain functional reorganization

Prismatic adaptation (PA) is a visuomotor procedure using prismatic lenses to induce a temporary shift of visuomotor coordinates. It relies on a brain network which includes the anterior and posterior cerebellum and parietal regions, such as the intraparietal sulcus and the posterior parietal cortex. Lesions in these parietal areas are often associated with the presence of Optic Ataxia (OA), a disorder of visually guided reaching movements. Studies report contrasting results concerning the effects of PA in OA patients, whereby some fail in adapting to prisms and others show preserved adaptation. Here, we describe behavioural and neurofunctional changes in a left hemisphere stroke patient with OA who completed ten sessions of leftward PA as part of her cognitive rehabilitation. After the treatment, reaching improved with the contralesional hand in the ipsilesional hemifield. Moreover, resting-state fMRI measures of network dispersion applied to low-dimensional functional gradients revealed marked hemispheric asymmetry, with greater reorganization in the left hemisphere involving an increase in network segregation in left attentional and somatosensory networks, alongside higher intra-hemispheric network dispersion. Conversely, inter-hemispheric dispersion decreased, particularly between attentive and somatosensory-motor networks. Dynamic edge-centric analysis showed reduced entropy in the visual network and increased entropy in the dorsal attention and control networks. These entropy shifts, reflective of nodal diversity in functional co-fluctuations, correlated with direct structural disconnections. Conversely, static gradient-based reorganization was significantly associated with indirect structural disconnection profiles. To our knowledge, this is the first study exploring changes at the behavioural and neurofunctional level in an OA patient following repetitive sessions of PA, highlighting complementary contributions of static and dynamic functional neuroimaging features in capturing possible mechanisms of functional reorganization.