Metabolic connectivity of freezing in Parkinson's disease

BackgroundFreezing of gait (FoG) is among the most disabling gait disorders of Parkinson's disease. The full understanding of its mechanisms requires a network study approach. So far, FoG was mainly studied using magnetic resonance imaging, and especially using the resting state functional sequence, which does not completely reflect the brain actual modifications.ObjectiveThis study aims to investigate metabolic networks using position emission tomography (PET) imaging. Exploration after a rest or gait session combined with a delayed tracer's uptake are assumed to reflect the actual metabolism modifications.MethodsTwenty-six patients in the off-drug state underwent two PET imaging sessions using [¹⁸F]- fluorodeoxyglucose, the first after 30 min of rest (rest condition) and the second after 30 min of real gait (gait condition). Twelve patients presented real FoG during cerebral glucose uptake. Brain connectivity matrices were measured for each group and condition, and then compared.ResultsIn the rest condition, the freezing group showed globally reduced metabolic connectivity between brain regions compared to the non-freezing group. During gait, enhanced connectivity was observed in the cerebellum, cerebello-cortical loops and parieto-frontal regions, with high recruitment of the visual cortex in the freezing group. However, connectivity inside cerebellar networks remained lower in the freezing group than in the non-freezing group, while occipito-frontal connectivity was higher in the freezing group.ConclusionsStudying real freezing of gait in a vertical position emphasized the role of the visual cortex and cerebellum in gait problems.