Primate translational vestibuloocular reflexes. III. Effects of bilateral labyrinthine electrical stimulation

Primate translational vestibuloocular reflexes. Ill. Effects of bilateral l abyrinthine electrical stimulation. J. Neurophysiol. 83: 1662-1676, 2000. T he effects of functional, reversible ablation and potential recruitment of the most irregular otolith afferents on the dynamics and sensitivity of the translational vestibuloocular reflexes (trVORs) were investigated in rhesu s monkeys trained to fixate near and far targets. Translational motion stim uli consisted of either steady-state lateral and fore-aft sinusoidal oscill ations or shortlasting transient lateral head displacements. Short-duration (usually <2 s) anodal (inhibitory) and cathodal (excitatory) currents (50- 100 mu A) were delivered bilaterally during motion. In the presence of anod al labyrinthine stimulation, trVOR sensitivity and its dependence on viewin g distance were significantly decreased. In addition, anodal currents signi ficantly increased phase lags. During transient motion, anodal stimulation resulted in significantly lower initial eye acceleration and more sluggish responses. Cathodal currents tended to have opposite effects. The main char acteristics of these results were simulated by a simple model where both re gularly and irregularly discharging afferents contribute to the trVORs. Ano dal labyrinthine currents also were found to decrease eye velocity during l ong-duration, constant velocity rotations, although results were generally more variable compared with those during translational motion.