Fig. 1: Spike transmission between two neurons can be estimated from spike times.

a Increased membrane potential variability increases spontaneous spiking. A leaky integrate and fire (LIF) model neuron was simulated with different levels of membrane potential variability, quantified by the noise SD, σ (n = 6 repetitions for each of n = 11 σ values, from 0 to 5 mV with 0.5 mV increments; each 180 min). The firing rate (λ₂) of the simulated neuron is shown for each σ value; here and in (b), error bands indicate SEM. The trace next to the cartoon shows 300 ms of simulated membrane potential, and the histograms show the distribution of membrane potentials (σ = 3 mV). b Even small-magnitude EPSPs induce observable spike transmission gain in the presence of noise. The simulated LIF neuron (2) was driven via an excitatory synapse by a presynaptic neuron (1) with Poisson spiking (λ₁ = 5 spk/s) modified by refractoriness. Synaptic conductance was modified to yield n = 11 different unitary EPSP (uEPSP) magnitudes (from 0 to 2 mV with 0.2 mV increments), and the real spike transmission gain (rSTG) was computed for every σ and uEPSP combination (n = 121). Both uEPSP magnitude and membrane potential variability control spike transmission. c A cross-correlation histogram (CCH; bins size: 1 ms) was computed from a pair of simulated spike trains as in (b); σ = 3.4 mV, uEPSP magnitude = 0.6 mV. For deriving an estimated STG (eSTG) from the CCH, the level of baseline joint counts (blue line) was first estimated using the “tails” predictor, averaging CCH values at time lags |τ| ≥ 11 ms. The spike transmission curve (STC; black line) was estimated as the above-baseline curve with a peak in the temporal region of interest (ROI; defined here as 0 < τ ≤ 5 ms; gray bins), with zeros in all other bins. The eSTG is the area under the estimated STC. d Spike transmission gain estimated from the CCH is an accurate estimate of the real STG. For every simulation run (n = 6 repetitions for each of 121 σ and uEPSP combinations), rSTGs and eSTGs were computed. Different colors correspond to different uEPSP magnitudes as in (b), and the black circle corresponds to the example in (c). Spearman’s correlation coefficient between eSTG and rSTG is ρ = 0.94 (n = 726 random samples, p < 0.001, permutation test).