Figure 4.

Variance increases at the population level before transitions in activity pattern. (A and B) Cartoon schematic depicting noisy ball attracted to bottom of trough. The same amount of noise induces larger deviations in (B) compared with (A). (C) Above: voltage trace from PD neuron in isolated pacemaker plotted in orange. Scale, 1 s, 5 mV at −50 mV. Below: phase portrait generated from low-passed voltage trace plotted in orange as normalized membrane voltage (Vm) versus normalized instantaneous change in voltage (dVm; see Materials and methods). The solid black line represents the mean of the oscillations, and the dashed black lines are two SDs plus and minus the mean. These values—means and SDs—are calculated for 200 points in phase schematized by the solid and dashed black and gray lines. (D) Each green line represents the moving average of combined coefficients of variation (see Materials and methods) plotted as a function of temperature from transition to silence (red line). (E and F) Each blue line represents the moving average of combined coefficient of variation as a function of pH. Experiments are aligned to transition. (E) Red line represents transition to tonic spiking. (F) Red line represents transition to silence. (D–F) Linear regression on log-transformed data predicting CCV using proximity to transition. To see this figure in color, go online.