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Abstract

The contribution of vestibular signals to postural, locomotor and oculomotor control has been widely investigated. Recently, vestibular signals have also been shown to contribute to the online control of reaching arm movements towards memorized visual targets. Indeed, when applied at the onset of the movements with standing subjects, galvanic vestibular stimulation significantly biased hand trajectory. In the present study, we tested whether a change in vestibular input also elicits modifications in arm trajectory when the subjects are seated, that is in a condition that has been reported to reduce the sensitivity to vestibular input. Subjects were seated, head-fixed, in complete darkness and were instructed to reach for memorized visual targets with the hand. In a randomly selected half of the trials, a 1.5sec-3mA galvanic vestibular stimulation (GVS) of variable polarity was triggered by the movement onset. Results revealed significant GVS-induced directional shifts of reaching movements towards the anode side. The earliest significant deviations of hand path occurred 310 ms after GVS onset. Mean directional errors with respect to control condition (i.e. movement without GVS) were –0.66° and 1.25° with the anode on the left and right mastoid, respectively. These deviations of hand trajectory corroborate the results previously obtained with standing subjects, supporting the idea that vestibular input participates to online control of the arm.