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EFFECTIVE CONNECTIVITY IN SUBCORTICAL VISUAL STRUCTURES IN DE NOVO PATIENTS WITH PARKINSON DISEASE

Background: PD is associated with non-motor symptoms appearing before the motor symptoms onset. Recent studies report dysfunctions of visual structures at early stages of PD. Objective: This study addresses effective connectivity in the visual network of PD patients. Methods: Using brain functional MRI and Dynamic Causal Modeling analysis, we investigated the connectivity between the superior colliculus, the lateral geniculate nucleus and the primary visual area V1 in 22 de novo untreated PD patients and six months after starting dopaminergic treatment compared to age-matched healthy controls. Results: Our findings indicate that the superior colliculus drives cerebral activity for luminance contrast processing both in healthy controls and untreated PD patients. The same effective connectivity was observed with neuromodulatory differences in terms of neuronal dynamic interactions. The modulation induced by luminance contrast changes of the superior colliculus connectivity (self-connectivity and connectivity to the lateral geniculate nucleus) was inhibited in PD patients (effect of contrast: p = 0.79 and p = 0.77 respectively). The introduction of dopaminergic medication failed to restore the effective connectivity modulation observed in the healthy controls. Interpretation: The deficits in luminance contrast processing in PD seem due to a deficiency in connectivity adjustment from the superior colliculus to the lateral geniculate nucleus and to V1. Administration of a dopaminergic treatment over six months was not able to normalize the observed alterations in inter-regional coupling. These findings highlight the presence of early dysfunctions in primary visual areas, which might be used as early markers of the disease.