Figure 1.

Nonlinear transfer of signal and noise correlations in vitro. A, Schematic diagrams illustrating variance gain and correlation gain. Each colored area corresponds to an equal increment on the horizontal axis. B, To mimic a typical sensory processing experiment with repeated presentations of an identical stimulus, we injected currents with a signal component that was the same on each trial, and a noise component that was different on each trial. Example membrane potential traces and spiking across trials for a typical neuron are shown. Action potentials were clipped for plotting. C, We injected Gaussian white noise currents into layer 2/3 pyramidal neurons in mouse V1 in vitro and analyzed the dependence of output signal and noise correlations on the variance and correlation of signal and noise inputs. We defined the input as the membrane potential fluctuations at the soma and the output as spike counts in 50 ms time bins. D, The input signal variances and output signal and noise correlations (top and bottom, respectively) that resulted from injecting currents with changing signal variance and fixed noise variance, signal correlation, and noise correlation. Pairs were grouped by input signal variance. The input signal variance for a pair of neurons was computed as the geometric mean of the input signal variances for each neuron. The numbers in parentheses above each data point indicate the number of pairs in each group. Error bars indicate 95% confidence intervals on the median value across all pairs in a particular group (estimated via bootstrapping). The mean input noise variance, input signal correlation, and input noise correlation were 20 mV², 0.4, and 0.25. E, The input SNRs and output signal and noise correlations that resulted from injecting currents with changing SNR and fixed correlations. Pairs were grouped by input SNR. The input SNR for a pair of neurons was computed as the geometric mean of the SNRs for each neuron. The mean values of the total input variance, input signal correlation, and input noise correlation were 25 mV², 0.5, and 0.35. F, The input signal correlations and output signal and noise correlations that resulted from injecting currents with changing signal correlation and fixed signal variance, noise variance, and noise correlation. Pairs were grouped by input signal correlation. The mean input signal variance, input noise variance, and input noise correlation were 4 mV², 8 mV², and 0.8.