Figure 9.

LFP estimation from time-clustered spikes. For each LFP recording site, we considered all the spike trains recorded within a sphere of radius R (r = 2 mm in A, D; r = 4 mm in B, E; r = 6 mm in C, F). For each spike, we asked whether there were spikes recorded from other electrodes within a distance R of the LFP and within τ ms (x-axis). We built a model spike train that contains all the spikes within R mm of the LFP and within τ ms of any nearby spike (temporally clustered spikes; red spikes in the scheme on top and red circles in A–F) and a separate model spike train that contains all the spikes within R mm of the LFP but without other spikes within τ ms (isolated spikes; blue spikes in the scheme on top and blue circles in A–F). These model spike trains were used to estimate the LFP using Equations 2–4. Here we report the estimation accuracies as a function of τ for different values of R for the two types of spike train models. The numbers indicate the average firing rates for the corresponding circles. The triangles indicate the estimation accuracy obtained under the null hypothesis. D–F, Part of the differences between temporally clustered spikes and isolated spikes in A–C are attributable the different firing rates between the two models. To control for the number of spikes, in D–F, we only considered those values of R, τ and those trials in which the number of spikes for the red circles was within 20% of the number of spikes for the blue circles.