Figure 5.
Dendritic spikes are highly attenuated and often occur within the somatic refractory period. A, Method used to measure attenuation of dendritic spikes during the complex spike. Top, Example response with an extra dendritic spike, recorded simultaneously in the dendrite (light blue; 142μm from soma) and soma (red; traces offset for clarity); also shown are dendritic and somatic averages of events without extra dendritic spikes but with similar somatic firing pattern (black). Bottom, Subtraction of these averages from the sweeps with extra spikes reveals the depolarization in the dendrite (light blue) and the soma (red) caused by the extra dendritic spike. The peak differences in depolarization were measured (blue arrows) at both locations, and attenuation was calculated as somatic depolarization as a percentage of dendritic depolarization. B, Attenuation of extra dendritic spikes in individual datasets (open symbols; red symbol indicates data shown in A) and in the whole population (blue bar; mean ± SEM). C, Illustration of the measurements made of dendritic spike time and resulting somatic event amplitude. Horizontal arrow, Time between the extra dendritic spike and the spike preceding the somatic event. Vertical arrow, Somatic event amplitude, measured as difference between preceding trough minimum and event maximum; this amplitude is normalized by the amplitude (above average baseline Vm) of the first spike of the complex spike. D, Dependence of somatic event amplitude on dendritic spike latency, as illustrated in C, for the data shown in Figure 3D. Red circles, Cases in which an extra dendritic spike failed to trigger a spike, generating only a subthreshold depolarization; blue circles, cases in which an extra spike triggered a somatic spike. The refractory trend is highlighted by a sigmoidal fit (black line); half- maximum = 1.7 ms. E, Dependence of somatic event amplitude on dendritic spike latency (n = 19 datasets), binned according to the time intervals marked by the x-axis ticks. Red and blue symbols are as in D. The refractory trend is highlighted by a sigmoidal fit to extra spike data, constrained to a baseline amplitude of 0; half-maximum = 1.4 ms.