1 Spatial and temporal properties of eye movements produced by 2 electrical stimulation of semicircular canal afferents 3 4

24 To investigate the characteristics of eye movements produced by electrical stimulation of 25 semicircular canal afferents, we studied the spatial and temporal features of eye movements 26 elicited by short-term lateral canal stimulation in two squirrel monkeys with plugged lateral 27 canals, with the head upright or statically tilted in the roll plane. The electrically-induced 28 vestibulo-ocular reflex (eVOR) evoked with the head upright decayed more quickly than the 29 stimulation signal provided by the electrode, demonstrating an absence of the classic velocity 30 storage effect which improves the dynamics of the low-frequency VOR. When stimulation was 31 provided with the head tilted in roll, however, the eVOR decayed more rapidly than when the 32 head was upright and a cross-coupled vertical response developed which shifted the eye’s 33 rotational axis towards alignment with gravity. These results demonstrate that rotational 34 information provided by electrical stimulation of canal afferents interacts with otolith (or other 35 graviceptive cues) in a qualitatively normal manner, a process which is thought to be mediated 36 by the velocity storage network. The observed interaction between the eVOR and graviceptive 37 cues is of critical importance for the development of a functionally-useful vestibular prosthesis. 38 Furthermore, the presence of gravity-dependent effects (dumping, spatial orientation) despite an 39 absence of low-frequency augmentation of the eVOR has not been previously described in any 40 experimental preparation. 41