Evidence for interactive locomotor and oculomotor deficits in cerebellar patients during visually guided stepping

Eight patients suffering from primary cerebellar degenerative diseases unde rtook a walkway task, demanding precise foot placement at each step, and a visual fixation task, requiring only eye movements. Step cycle and horizont al eye movements were recorded throughout the tasks and compared to those o f healthy adults (including age- and ses-matched controls). Cerebellar pati ents displayed both locomotor and oculomotor deficits. Increases in duratio n of the stance, swing and double support phases of the step cycle were all shown to contribute to ataxic gait. Dysmetric saccades to fixate the footf all targets were seen more frequently in patients than in controls. These h ypometric saccades were followed by one or more corrective saccades (patien ts: >45% accompanied by one or more corrective saccades; controls: <10% acc ompanied by a single corrective saccade). Similarities between the oculomot or deficits displayed by patients during the visual fixation task and when walking indicate that the latter ale not merely a consequence of ataxic gai t. The existence of several links between these locomotor and oculomotor de ficits provides evidence for considerable interaction between the two cont: ol systems in the production of patterned eye and stepping movements. These results also suggest that the cerebellum plays an active role in the co-or dination of visually guided eye and limb movements during visually guided s tepping.