Celeste Cafaro¹ (), Alessio Fracasso², Ciro Rosario Ilardi³, Marco Cerrone⁴, Giovanna Vermiglio⁵, Carlo Cavaliere⁴, Giovanni Cirillo⁶, Antimo Buonocore¹; ¹Suor Orsola Benincasa University, Italy, ²University of Glasgow, ³University of Naples Federico II, Italy, ⁴IRCCS Synlab SDN, Italy, ⁵University of Messina, Italy, ⁶University of Campania Luigi Vanvitelli, Italy

Oculomotor deficits are a hallmark of Parkinson's disease (PD) and provide important insights into its associated visual, motor, and cognitive dysfunctions. For instance, antisaccade tasks—which require redirecting gaze to the opposite location of a cued target—have been widely used to describe reduced inhibitory control. However, the impact of PD on reflexive oculomotor inhibition, independent of cognitive control, remains unclear. We hypothesized that saccadic inhibition (SI), which relies on oculomotor structures known to be impaired in PD patients, may more accurately reflect disease progression. These measures are less influenced by cognitive abilities, making them promising candidates as biomarkers for the condition. To test this hypothesis, we assessed eye movements in eleven PD patients (including three de novo cases) and six healthy controls (HCs) across classic oculomotor tasks, including visually guided saccades, prosaccades, antisaccades, smooth pursuit, and visual search. The latter two tasks were modified by introducing visual transients to evaluate SI. As expected, PD patients exhibited hypometric saccades and slower reaction times in visually guided saccade tasks compared to HCs. In the antisaccade task, PD patients failed to inhibit responses to cued targets and displayed high inter-participant variability. Smooth pursuit performance showed reduced gain and an increased intrusion of catch-up saccades. Interestingly, both groups exhibited fast SI in response to visual transients, suggesting preserved reflexive inhibitory abilities in PD. However, SI in PD patients was weaker and lasted longer, followed by a diminished rebound phase, suggesting deficits in oculomotor reprogramming. A similar SI pattern was observed for catch-up saccades during smooth pursuit. Unlike the antisaccade task, reflexive inhibitory measures were consistent across PD patients and distinguishable from HCs, including the de novo cases. These findings suggest that SI measures in visual search tasks may be effective for the early detection of deficits in PD and potentially other neurodegenerative disorders.

Acknowledgements: C.C, G.V., G.C, A.B. were supported by a grant from the Italian Minister of Research and University (PRIN PNRR 2022 P2022ST78T).