Sparse balance: Excitatory-inhibitory networks with small bias currents and broadly distributed synaptic weights
Fig 3
Asynchronous irregular activity in the sparse balance model.
A) Responses of network neurons in time for four different nonlinear response functions: Heaviside step function, rectified tanh, rectified linear, and rectified quadratic. B) Rates ϕ(x) (dark) superimposed on the currents x (light) for four example units. Cells respond robustly and infrequently across choices of the response functions. The synchrony index, as defined in [19], is approximately 10−4 for each of the networks shown. C) Fractions of active neurons, or the inverse sparsity. D) Normalized distributions for the fraction of ON-time, defined as the fraction of (simulation) time a unit spends above threshold. For better visualization, histograms are smoothened using kernel density estimation. E) Normalized distributions of x, showing non-Gaussian dynamics. F) Population-averaged autocorrelation functions of x. At this fixed value of in-degree (K = 1000), all response functions produce qualitatively similar results. (Model parameters: g = J0 = I0 = 2, Jij ∼ gamma, N = K).