Pre-saccadic Rise Neurons In The Hindbrain Control The Timing Of Spontaneous Saccades

The spontaneous generation of saccades and fixations provides a simple model for understanding how internal brain dynamics are linked to behavior. We coupled calcium imaging with focal laser ablations in larval zebrafish to comprehensively map the activity patterns underlying the generation and control of this spontaneous behavior. We found a continuum of activity types ranging from cells that burst only during saccades, to cells that displayed tonic discharge during fixations, to neurons whose activity rose in advance of saccades by multiple seconds before falling to baseline after saccade completion. The activity of these pre-saccadic rise neurons was predictive of upcoming saccade time when analyzed under the general framework of ramp-to-threshold models. Ablations in regions where these neurons were densest led to the greatest delay in saccade initiation. The rate of rise in these neurons was variable across cells and fixations, with increased slope coupled to shorter rise times. These findings suggest that the novel class of pre-saccadic rise neurons presented here are involved in the timing of self-initiated saccadic movements.