Figure 7.   A dynamic dendritic refractory period interacts with somatic ISI to regulate burst output. A, A modified LIF model that links spike duration with refractory period reproduces an increase in spike frequency with applied current until reaching a threshold for switching from tonic to burst discharge (200 msec pulse). Frequency on the y-axis is measured in units of the inverse membrane time constant. Parameters are A = 0.15, B = 2,  = 1, r_s = 0.1,  = 20,  = 0.35,  = 0.05, D = 0.1, E = 3.5. B, C, Soma-dendritic interactions for applied currents that evoke either tonic discharge (B; I = 1.18) or burst discharge (C; I = 1.21). Top, Somatic voltage; second row, b, the variable used to control both dendritic spike duration and dendritic refractory period; third row, the effective spike-induced current flowing from dendrite to soma, s[t  t_n, b(t)]  s(t  t_n, ); bottom: somatic ISI (open circles; t_n  t_{n  1} is plotted at t = t_n) and dendritic refractory period (r) (filled circles). In the voltage trace (C), asterisks indicate spike doublets and arrows indicate burst AHPs. Note that burst discharge is invoked at each juncture of a decreasing somatic ISI and an increasing dendritic refractory period (C, bottom, open arrows). Parameters are A = 0.15, B = 2,  = 1, r_s = 0.1,  = 20,  = 0.35,  = 0.05, D = 0.1, E = 3.5.