Encoding of Eye Position in the Goldfish Horizontal 4 Oculomotor Neural Integrator

35 36 Monocular organization of the goldfish horizontal neural integrator was studied during 37 spontaneous scanning saccadic and fixation behaviors. Analysis of neuronal firing rates revealed 38 a population of ipsilateral (37%), conjugate (59%) and contralateral (4%) eye position neurons. 39 When monocular optokinetic stimuli were employed to maximize disjunctive horizontal eye 40 movements the sampled population changed to 57%, 39%, 4%. Monocular eye tracking could be 41 elicited at different gain and phase with the integrator time constant independently modified for 42 each eye by either centripetal (leak) or centrifugal (instability) drifting visual stimuli. Acute 43 midline separation between the hindbrain oculomotor integrators did not affect either 44 monocularity or time constant tuning corroborating that left and right eye positions are 45 independently encoded within each integrator. Together these findings suggest that the 46 ‘ipsilateral’ and ‘conjugate/contralateral’ integrator neurons primarily target abducens 47 motoneurons and internuclear neurons, respectively. The commissural pathway is proposed to 48 select the ‘conjugate/contralateral’ eye position neurons and act as a feedfoward inhibition 49 affecting null eye position, oculomotor range and saccade pattern. 50 51