Lisa Bauer¹, Joseph C. Donovan¹, Herwig Baier¹; ¹Max Planck Institute for Biological Intelligence

Saccadic eye movements are fundamental to vertebrate visual perception, yet it is still unclear exactly how circuits smoothly process the resulting shifts in visual input. The zebrafish model, with its experimental tractability, offers an ideal system for investigating the underlying sensorimotor circuits. Zebrafish perform spontaneous and visually induced saccades as early as 4 days post fertilization (dpf). Here, we combined eye tracking and two-photon calcium imaging to investigate the neuronal correlates of saccades in larval zebrafish (6-8 dpf). We focus on the optic tectum (OT), the fish equivalent of the mammalian superior colliculus (SC), as well as the largest visual brain area. Using a two-photon microscope custom-modified with a remote focusing path to enable rapid multi-plane imaging, we record single-cell resolution neuronal activity across the OT at 5 volumes per second. Even in the absence of visual stimuli we find neurons in the OT that showed increased activity correlated with spontaneous saccades. To investigate how visual stimuli are integrated, we recorded from the same neurons during various visual stimulus paradigms. Our findings reveal that most spontaneous saccade-correlated neurons in the OT respond similarly regardless of visual environment. Moreover, spontaneous saccade-responding neurons are a subset of visually induced saccade neurons. Notably, while many neurons were active around the time of a saccade, certain neurons’ activity peaked before, suggesting a role in anticipatory motor planning. Our results underscore the effectiveness of the larval zebrafish as a model for functional investigation, enabling experimental approaches that are challenging to implement in primate models.