Gait initiation in bilateral vestibular loss

Gait initiation is a transient procedure between orthostatic posture and steady-state locomotion and includes anticipatory anteroposterior (AP) and lateral movements. Commands for this task are located in some levels of brain stem, which modulates activity of central pattern generator in the spinal cord. The purpose of this work was to explore the role of the vestibular system in this voluntary stepping.

Six patients with chronic bilateral vestibular loss (BVL) were measured by means of a large force plate (70 cm x 120 cm ) and the displacement of the center of pressure (COP) during gait initiation was calculated. Measurement parameters comprised maximum distance (MD), velocity (MV) in the AP and lateral direction as well as for pre-, first- and second-step stages, and the angle of the COP trajectory.

For all stages, BVL patients registered lower values for both MD and MV in the AP direction than did normal subjects. In the lateral direction, however, neither MD nor MV in BVL patients showed any difference from those of normals. The step angle of the COP trajectory was obviously reduced.

These results suggest that in the AP direction, the vestibulospinal pathway can influence the locomotor related neural circuits, including the central pattern generator and supraspinal levels, by means of modifying the velocity and step length in order to stabilize the trunk. On the other hand, the control mechanism in the lateral direction may be different from that in the AP direction.