Effects of task constraints on obstacle avoidance strategies in patients with cerebellar disease.

The present study examined the effects of cerebellar disease on the organization and execution of obstacle avoidance tasks. To this end, we characterized how variations in the execution demands of the subsequent obstacles in multiple obstacle crossing tasks influenced the stepping performance of the initial obstacle in patients with cerebellar degeneration (CD) by manipulating the height (6 cm and 16 cm) and distance (1 m and 2 m) of the second obstacle. Nine patients with bilateral cerebellar atrophy and nine age-matched normal controls were instructed to walk along an 8 m long pathway and step over two obstacles without contacting them. The primary finding indicated that CD patients exhibited an elevated foot clearance over the initial obstacle when the height demand of the second obstacle was increased. Such abnormal step-height adjustments in CD patients are considered as an adaptive avoidance strategy to diminish the execution demands of complex obstacle tasks and to enhance safe performance. These results suggest that the cerebellum is important for the implementation of optimal stepping strategies to be used during multiple obstacle crossings in which the obstacles have different execution demands.