Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, C7

Oral Communications

Visuo-vestibular influences involved in the broken escalator phenomenon' gait after-effect (GAE)

Bunday, Karen Louise; Bronstein, Adolfo M;

1. Movement and Balance, Imperial College, London, United Kingdom.

The broken escalator phenomenon, the odd balance sensation experienced when walking onto an escalator which is stationary, is an after-effect of gait adaptation (1). This gait after-effect (GAE) demonstrates dissociation between knowledge and action as it occurs despite full awareness that the escalator will not move. This study investigates visuo-vestibular influences on this GAE. The experiments involved three sequential conditions: (1) walking onto the stationary sled (BEFORE); (2) walking 15 times onto a moving sled (MOVING) at 1.3m/s; and (3) a second set of stationary trials (AFTER) with clear warning that the platform will NOT move. In experiment 1 we tested 9 labyrinthine-defective subjects (LDS) and 13 age-matched normal controls. In experiment 2, 5 LDS and 5 age-matched controls repeated the experiment but, in the AFTER trials, subjects first walked blindfolded and then with full vision (eye re-opening). Gait velocity, trunk position, foot contact and leg EMG were measured. (i) The LDS were, as expected, significantly more unsteady during MOVING trials. During AFTER trials, both patients and control experienced an after-effect, shown as increased gait velocity and a forward trunk overshoot, with eyes open or closed. (ii) No significant group differences in the after-effect were present. (iii) However, re-opening the eyes in experiment 2 induced a significantly larger after-effect (trunk overshoot) in the LDS. In conclusion, (i) confirms the prominent role of the vestibular system during external postural perturbations (as in the MOVING trials). (ii) When the perturbation is internally generated, as in the AFTER trials, the CNS relies less on sensory feedback and more on feed-forward mechanisms to maintain balance. (iii) Re-emergence of the after-effect on eye re-opening reveals the existence of a high order visual context component in locomotor learning, which is enhanced in the absence of vestibular function.

Where applicable, experiments conform with Society ethical requirements