Cortical control of voluntary saccades in Parkinson's Disease

In Parkinson's Disease (PD) several aspects of saccades are affected. The saccade generating brainstem neurons are spared, however the signals they receive may be flawed. In particular volitional saccades suffer, but the functional anatomy of the impairment of saccade related cortical control is unknown.

We measured blood-oxygenation-level-dependent (BOLD) activation with fMRI while healthy participants and participants with PD performed volitional saccades between peripheral visual targets or fixated centrally. We compared saccade related BOLD-activity vs. fixation in participants with PD and in healthy controls and correlated perisaccadic BOLD-activity in PD patients with saccade kinetics (multistep saccades).

Saccade related BOLD-activation was found in both, PD and healthy participants in the superior parietal cortex (PEF) and the occipital cortex. Our results suggest remarkable hypoactivity of the frontal and supplementary eye fields (FEF and SEF) in PD-participants. On the other hand, PD-participants showed a more reliable BOLD modulation than healthy participants in the posterior cingulate gyrus, the parahippocampal gyrus, inferior parietal lobule, precuneus and in the middle temporal gyrus.

The absence (below threshold) FEF and SEF activation in PD patients performing volitional saccades is consistent with a cortical impairment of volitional movements in PD. Given the paradigm of this study and normal PEF responses, our results suggest that in PD a frontal neuronal circuitry, underlying saccade planning, selection and predicting a metric error of the saccade, is deficient.