For the analysis of GABAergic cells (Fig. 6), dendrites were traced using ‘Simple neurite tracer’ in ImageJ63. The program outputs a 1D sequence of coordinates traversing a dendrite and a 2D mask covering the traced dendrite, which were used to define ROIs along the dendrite (size, 1.5 μm of dendritic length; spacing, 1 μm). Visual responsiveness and orientation selectivity index were computed for individual ROIs. A region of dendrite is considered orientation selective if its response to least one stimulus orientation is significantly different from other orientations (p < 0.01, ANOVA across 8 conditions). Because synaptic and BAP signals were intermixed in the same dendritic compartment, no attempt was made to isolate synaptic signals from BAP-related components. We did not analyze the relationship between integrated synaptic signals and the output tuning in GABAergic cells.
