Vestibular contributions across the execution of a voluntary forward step.

This work addressed the influence of information arising from the vestibular system on the dynamic control of a forward step. Six subjects performed the stepping task with their eyes closed under three conditions of bipolar, binaural galvanic vestibular stimulation (GVS), including (1) no GVS, (2) GVS with the anode electrode on the side of the swing limb, and (3) GVS with the anode electrode on the side of the stance limb. GVS was delivered 1,500 ms prior to a cue to step. Ground reaction forces were collected from three force platforms and movement was recorded from IRED markers placed bilaterally on the body. The results showed that, following slight deviations caused by GVS onset, the step initiation behaviour was unaffected, but lateral deviations were found during the latter, more dynamic, phases of stepping for centre of mass trajectories, time integrals of the centre of pressure displacement and upper body roll. These findings showed that vestibular information is used differently across the execution of a step without vision. While the initiation phase is run in a feedforward manner without vestibular influence, vestibular information appears to be upregulated during the more dynamic phases. Also, the level of up-regulation may be different across step execution.