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Fig. 5 Individual Pretectum Neurons Represent Visual Motion Stimuli According to Their Effect on Optomotor Behaviors (A) Schematic of the model architecture (STAR Methods). Mean behavior regressors were first convolved with a temporal kernel that emulated measurable responses in our calcium imaging experiment. The regressors were then combined as a weighted sum, and a final thresholding step captured the non-negativity of the measured pretectal responses. We use N, F, L, and R to denote the Non-specific stimulus-on regressor, the Forward swim frequency regressor, and the Left/Right turn frequency regressors (STAR Methods). For compactness, we illustrate the procedure for the first three stimuli only. (B) Distribution of R-squared values (fraction of variance explained by the model) for all activated ROIs. Note that when the responses of AF5&6 units were fitted similarly, the fraction of variance explained was shifted toward smaller values in comparison with the pretectum case. (C) R-squared maps showing that the quality of model fits was comparable throughout the pretectum. As in Figure 3, we show coronal (center), transverse (top), left sagittal (left), and right sagittal projections (right) overlaid on anatomical maps (grayscale). A indicates the anterior-posterior axis, V the ventral-dorsal axis, and L the left-right axis. Scale bar represents 0.05 mm. (D) Example traces for four pretectum ROIs, together with associated model fits and R-squared values. The first two example ROIs show pretectal neurons that respond to glider stimuli with magnitudes closely matching the behavioral turning frequencies induced by the stimuli. The final two ROIs show that other pretectal neurons responded relatively non-selectively to glider stimuli. (E) Weight coefficient maps for the four regressors used in the model. ROIs utilizing the L or R regressors were localized to the left or right pretectum, respectively. ROIs receiving positive drive from the N or F regressors were localized to the anterior pretectum. All graphical conventions match (C). See also Figures S4 and S5.