Fig. 3. Single-spike firing pattern is characterized by a stable and narrow subthreshold membrane potential dynamic range.
a Representative recording of spontaneous in vivo electrical activity from a dopamine neuron in the VTA. The upper trace displays action potentials during a stable recording for >60 s. As in Fig. 2, blue dots in the lower trace represent Vmin while green dots represent Vthr. b Immunocytochemical identification demonstrates the recorded neuron (red) as TH-positive (green) within the VTA (arrow). Depiction shows the location of the recorded neuron (large red dot) in relation to all the recorded neurons in this study (gray and black dots). Black dots represent the locations of all the neurons that fired with a low Vmin BC (lower 10%). c Distribution of all Vmin from the cell in a, b, demonstrating a unimodal distribution (blue line = single Gaussian fit). d Distribution of all subthreshold voltage maxima (Vthr) from the cell in a, b, demonstrating a unimodal distribution (green line = single Gaussian fit). e Scatter plot of the interspike interval (ISI) versus Vmin (blue) and Vthr (green). f High temporal resolution of single-spike firing pattern (upper panel), and a mean spike-triggered pacemaker pattern (black trace in lower panel) with overlaid (gray) traces. g Histogram of the instantaneous firing rate for the cell in a, b. h Histogram of instantaneous firing rate for all cells with a low Vmin BC. i Example trace from the cell firing in a single-spike pattern with three action potentials in order from black, then orange, then red. Inset illustrates where the threshold occurs for the black action potential. j The phase plots for each action potential are displayed in the same color scheme as in i (black, orange, and red; plots are nearly completely overlapping). k Summary data of the changes in threshold voltage (left) and maximal depolarization rate (Max dV/dt; right) across the sequence of three action potentials for all cells firing with a low Vmin BC (two-sided Wilcoxon signed-rank test).