Model predictions of spike rate responses also show strong proximal-distal asymmetry.

A,B, Somatic responses to 50 Hz independent Poisson inputs delivered to 3 (blue), 6 (green), and 9 (magenta) distal synapses centered at 190 µm in (A) and 17 (blue), 21 (green), and 25 (magenta) proximal synapses centered at 90 µm in (B). C, Mean firing rates for distal drive with proximal modulation increasing from curve to curve (averages of 20 runs). Slope changes are accentuated by black bars centered at point of maximum slope. Colored squares correspond to traces in (A–B). D, Same as (C), but for proximal drive with distal modulation. Black bars accentuate left shifting of i-o curve. E, F, Similar input configuration to (C–D), but with proximal and distal inputs (same distances) on two different dendrites. Modulatory effect from both perspectives is linear, as evidenced by the nearly constant additive (vertical shifting) effect of either proximal or distal cross-branch modulation acting on the driver's input-output curves. G, Diagram illustrates driver-modulator interaction shown in (C). Proximal synapses when viewed as contextual modulators (left) lower the threshold θ and increase the gain α of the dendritic sigmoid nonlinearity. Distal synapses viewed as modulators (right) exert a left-shifting (threshold lowering) effect. Note diagrams are schematic representations of the modeling results; absolute and relative positions of the driver and modulator inputs in the schematics should not be given a literal spatial interpretation.