Gaze and Postural Reorientation in the Control of Locomotor Steering After Stroke

Background. Steering of locomotion is a complex task involving stabilizing and anticipatory orienting behavior essential for the maintenance of balance and for establishing a stable frame of reference for future motor and sensory events. How these mechanisms are affected by stroke remains unknown. Objectives. To compare locomotor steering behavior between stroke and healthy individuals and to determine whether steering abilities are influenced by walking speed, turning direction and walking capacity in stroke individuals. Methods. Gaze and body kinematics were recorded in 8 stroke and 7 healthy individuals while walking and turning in response to a visual cue. Horizontal orientation of gaze, head, thorax, pelvis, and feet with respect to spatial and heading coordinates were examined. Results. Temporal and spatial coordination of gaze and body movements revealed stabilizing and anticipatory orienting mechanisms in the healthy individuals. Changing walking speed affected the onset time but not the sequencing of segment reorientation. In the individuals with stroke, abnormally large and uncoordinated head and gaze motion were observed. The sequence of gaze, head, thorax and pelvis horizontal reorientation also was also disrupted. Alterations in orienting behaviors were more pronounced at the slowest walking speeds and turning to the nonparetic side in 3 of the most severely disabled individuals. Conclusion. The results in this convenience sample of slow and faster walkers suggest that stroke alters the stabilizing and orienting behavior during steering of locomotion. Such alterations are not caused by the inherently slow walking speed, but rather by a combination of biomechanical factors and defective sensorimotor integration, including altered vestibulo-ocular reflexes.