Figure 4. Spread of inhibition along a dendritic branch. A, Schematic of recording configuration, where blue spots indicate GABA uncaging at different distances from the main apical dendrite (Δx = 0, 10, 20, 30, and 40 μm). B, IPSCs evoked by GABA uncaging at different distances from the main apical dendrite, where the blue arrow indicates uncaging pulse. C, Left, Summary of IPSC amplitude versus uncaging distance, where dotted line indicates average exponential fit. Right, Space constants for individual cells (open circles) and mean ± SEM (closed circle). D, Similar to A with GABA uncaging at different distances (Δx = 0, 10, 20, and 30 μm) from the distal apical dendrite, where the dotted box indicates location of imaged spines and dendrites. E, Average Ca2+ signals evoked in apical spines by AP alone (black) or AP paired with GABA uncaging (red) at different distances from the imaging location, where the blue arrow indicates uncaging pulse and the black arrow indicates AP firing at 10 ms delay. F, Summary of impact of GABA uncaging at different distances on AP Ca2+ signals in spines (left) and dendrites (right). *p < 0.0125. G–I, Similar to D–F with GABA uncaging at centered, distal, or proximal locations along a dendritic branch; *p < 0.0167.