Figure 3. Continuum of intrinsic electrophysiological properties in SNr.

Whole-cell patch-clamp recordings of SNr neurons in vitro (120 cells).

(A) Top: Representative current-clamp trace of spontaneous SNr firing. Bottom: histograms of spontaneously firing rates (mean = 21 ± 15 Hz) and inter-spike interval (CV = 0.1 ± 0.1) in SNr.

(B) Left: three example action potential waveforms and the mean waveform (bottom) overlaid with all recorded waveforms (grey). Right: action potential waveforms in SNr neurons are characterized by highly correlated rise and fall durations.

(C) Left: 1-s depolarizing current step injected into an SNr neuron evokes a sustained higher firing. Middle: evoked firing rates increase as a linear function of current over a wide range. Right: across the SNr populations, the capacity to sustain fast-firing and the sensitivity to current inputs (neuronal gain) varied over a >10 fold range, but the mean firing responses increased linearly to depolarization in all neurons (R² = 0.99 ± 0.01).

(D) Non-linear firing responses to hyperpolarizing inputs in two neurons, which display (left) modest and (middle) robust post-inhibitory rebound firing from a 10-Hz baseline rate. The SNr population displays heterogeneous responses to hyperpolarization, quantified as the first post-inhibitory instantaneous rate and the rate sustained over 200 ms.