Fig. 1.

Setup and circuit overview. a Simplified circuit schematic for horizontal eye movements. Red dashed rectangle represents imaged brain area; blue cones show location of Mauthner cells. ABN, abducens nucleus; B, burst neurons; Dien, diencephalon; INN, internuclear neurons; IO, inferior olive; LR, lateral rectus; MB, midbrain; MN, motoneurons; MR, medial rectus; OMN, nucleus oculomotorius; OI, oculomotor integrator; PT, pretectum; rh 4–8, rhombomeres 4–8; VSM, velocity storage mechanism; Θ, eye position. Note that the connection from the VSM to the ABN in zebrafish is probably indirect [7]. Dashed arrows indicate direct or indirect inputs from upstream visual brain areas [8, 9]. a’ Simplified schematic response profiles for hindbrain oculomotor neurons during eye position changes. Dashed line represents an eye position or velocity of 0. L, left; P_L/R, Position coding neurons left/right, note that P_L and P_R have different firing thresholds; R, right; V_F, fast (burst) velocity neurons; V_S, slow velocity neurons. b Schematic of microscopy setup. Agarose-embedded zebrafish larvae were visually stimulated, while eye movements were recorded from below, and cellular calcium signals were recorded from above via a two-photon microscope. Setup not drawn to scale, binocular zone excluded for experiment with monocular stimulation only, scale bar 50 μm, red dashed rectangle represents imaged brain area, red arrows show GCaMP expression in the nuclei of the Mauthner cells, which served as a landmark (blue cones in a and in cell maps). A, anterior; L, left; P, posterior; PMT, photomultiplier tubes; R, right