Fig. 2.

Axonal spike initiation for middendritic electrode position causes a delayed backpropagating dendritic AP (A) but fails for a stimulus pulse with doubled amplitude (B). Display as in Fig. 1C but to account for numerical reasons with an increased amount of shorter dendritic compartments. Time courses of selected compartments are redrawn in the bottom. Note the 110 mV increase of the closest compartment to the electrode (purple) in (A) which causes enough subthreshold activities in the proximal dendrite compartments to cross the soma and to initiate a spike in the AIS. No depolarizing response reaches the soma in case (B) in spite of larger membrane amplitude at the most excited part of the dendrite. Dashed lines indicate the sodium current thresholds for the dendrite (Na_v1.2, 40 mV above V_rest) and the AIS (Na_v1.6, 20 mV above V_rest), the diameter of the dendrite is 5 μm, x_electrode=−200 μm, z_electrode=50 μm.