Figure 6.
A, The maximum and minimum of the normalized membrane potential Vm in the presence of a spatially inhomogeneous and oscillating extracellular field Ve. The colored areas indicate the Vm amplitude along the cable for dc (gray area), and ft = 100 (green area) and 200 Hz (red area). As expected for a low-pass membrane, for increasing values of the temporal frequency ft (arrows), Vm follows less and less the Ve oscillation. B, The effect of the time-dependent harmonic excitation on Vm as described through the normalized deviation β(Vm). As long as β(Vm) ≈ 0, the membrane response remains quasistationary. Once β deviates from zero, low-pass filtering affects the overall process. The results are shown for the basal dendrite (crosses), the soma (circles), the proximal apical dendrite (squares), the medial apical dendrite (diamonds), and the distal apical dendrite (x) in black color. The excitation was spatially centered at the middle of each section. For a typical value of τm = 20 ms, (2π ft τm)1/2 = 1 and 5 are equivalent to ft ≈ 8 and 200 Hz, respectively. β(Vm) is also shown for the unbranched cable case (red line) for comparison.