Whole-brain response profiles to the water flow stimuli. A, The first group of responses show a rapid response to the onset of the stimuli, indicated by colored rectangles (mean responses, SD shaded area). Some responses are weakly direction selective (top), the others are selective to h-t (middle) or t-h (bottom) water flow. Outlines indicate telencephalon (Telen), OT, TS (dotted), and MON. Scale bar, 100 µm. Rotation in Multimedia 1. B, The second group shows ongoing responses for the duration of the stimuli (mean responses, SD shaded area). These can again be subdivided by their direction selectivity: weakly h-t (top), strongly h-t (middle), or strongly t-h (bottom). Rotation in Multimedia 2. C, The third group shows a slow buildup of the GCaMP signal, peaking at the end of the stimuli. Only two such clusters fit into this category: one strongly selective for h-t flow and the other strongly selective for t-h flow. Rotation in Multimedia 3. D, Scatter plot of the average DSI of each cluster. DSI = 0.16 ± 0.13, 0.83 ± 0.07, −0.66 ± 0.23, 0.30 ± 0.19, 0.93 ± 0.03, −0.87 ± 0.07, 0.9 ± 0.07, −0.84 ± 0.1; mean ± SD, n = 13 fish). The p values of KS tests against normal distribution (µ = 0, σ = 0.2) = 2.4981e-02, 1.8228e-04, 5.9128e-12, 5.8589e-12, 7.6683e-13, 5.9769e-11, 5.9260e-12, 6.3809e-12. E, Scatter plot of the average time to maximum intensity of each cluster, both for the h-t (left) and t-h (right) stimuli (2.3 ± 1.1, 4.3 ± 0.9, 2.4 ± 0.7, 4.7 ± 0.5, 10.2 ± 1.2, 13.7 ± 3.4, 13.7 ± 4.6, 8.3 ± 5.6; mean ± SD, n = 13 fish). F, tSNE plot of all the members from the eight clusters, using correlation as a distance. 3-dimensional rotations of the dorsal views shown in A, B, and C can be found in Movies 1, 2, and 3, respectively.