Fig. 1.

External stimulation at the dendrite. (A) geometry. (B) high threshold Na_v1.2 channel densities represented by the maximum conductance (magenta) exist in the upper part of the neuron until AIS and low threshold Na_v1.6 channels (purple) from AIS until the axon terminal. Note that high concentrations from axon hillock until myelination exceed even that of nodes of Ranvier by a factor 2 whereas in soma and dendrite a uniform maximum sodium conductance of 8 mS/cm² is assumed (Hu et al., 2009). (C) Transmembrane voltages as functions of time. Electrode tip is assumed 300 μm from the soma and 80 μm from the axis (x_el=−300 μm, z_el=80 μm) in a homogeneous medium with resistivity ρ_e=300 Ωcm. At this distance the electric field has a direct depolarizing effect only within the gray shaded region where the slopes at stimulus onset in (C) are positive. Spike is initiated in the compartment closest to the electrode (cyan) and propagates in both directions. When intracellular currents cross the soma (red) they activate the low threshold region and cause earlier AP peaks thereof compared to the soma and the last presomatic dendritic compartments.