To explore neural substrates of visual-spatial dysfunction in Parkinson’s Disease (PD).

In PD, abnormal ocular-motor function can affect visual exploration strategies, while restricted visuospatial processing may negatively influence motor function.

Cross-sectional analysis of 18 PD patients and 14 matched controls (HC). Ocular motor function was recorded by a binocular eye tracker (Eye Link-II) during the Benton Visual Recognition Test (BVRT). Visuospatial function was assessed by MoCA, Rey-Osterrieth Figure (RFT), and computerized tests (Navon Test, Visual Search, Visual Reaction). MDS-UPDRS, Pegboard Test and Timed Up and Go Test (TUG) assessed motor function. Patterns of functional connectivity (FC) on resting-state fMRI were investigated within the dorsal attention (DAN), executive control (ECN), fronto-occipital (FOC), primary and secondary visual networks, through independent component analysis. Partial correlations were performed with age and gender as covariates between clinical and FC outcomes. Variables showing a Pearson coefficient ≥ ±0.75 were considered significant.

PD subjects showed poorer performance on UPDRS-III (p<0.002), Pegboard Test (p<0.002), TUG (p<0.003), and Navon Test (number of errors, p<0.003) [table #1]. A trend towards worse scores in RFT was observed (p= 0.09). During BVRT, PD patients generated more saccades and longer path lenghts to complete the task [table #2]. PD patients exhibited higher FC levels within the DAN and ECN (p<0.001, adjusted for cluster size). In both groups performances on MoCA strongly correlated with FC in the DAN, FOC and ECN. In HC, performances on Navon Test correlated with FC in the FOC. In PD performances on TUG correlated with FC in the ECN.

Evidence of impaired ocular-motor exploration and altered cognitive processing of visual information was found in PD. These findings were accompanied by stronger FC in brain networks involved in top-down attentional control of perceptual information. These changes may reflect compensatory mechanisms boosting attentional resources to preserve motor-cognitive function in these patients.