O.G. Debowy; E. Aksay; G. Major; R. Baker; H.S. Seung; D.W. Tank Horizontal eye position stability is attributed to activity in a velocity-to-position neural integrator (VPNI) consisting of 2 nuclei located bilaterally in the caudal hindbrain of the goldfish. Prior work suggests that each VPNI nucleus has ipsi-excitatory and contra-inhibitory projections with similar connections to the abducens nuclei. To test if eye position stability could be maintained by each integrator functioning independently, a surgical interruption of the midline was performed and verified later by histology. Eye positions were measured in awake, restrained animals and stability monitored in the absence of visual input. Post-lesion goldfish demonstrated a conjugate spontaneous scanning saccadic pattern, but the oculomotor range was reduced as compared to that in light. Position-velocity (P-V) plots showed null points were shifted nasally with eye position drift towards null in 6/7 fish; in one case, a temporal shift in null and eccentric drift was observed. The time constant , determined from the inverse slopes of the best fit regression lines in P-V plots, was reduced acutely from 30s (controls) to a minimum of 4s, but increased rapidly within days to a range of 9-36s (18.7s10.5, n=5) clearly demonstrating integrator persistence. When intersaccadic eye velocity slip, proportional to eccentric eye position, was added through use of visual feedback (5-14d), was modifiable and fixations could become either unstable or leaky, diverging from or converging towards null, respectively. These data suggest that ipsi-excitatory feedback within each VPNI is sufficient to produce persistence as well as plasticity. Supported by: Lucent, NSF and NIH