Figure 3.

Effect of additional synchrony at slower oscillation frequencies. A, Spike histograms and the resulting stratum pyramidale extracellular potentials for three different widths, represented by standard deviation σ of 1 (red), 2 (green), and 4 (blue) ms, in the Gaussian-shaped bursts of spiking in the population during a 50 Hz rhythm. At low σ (high synchrony) the extracellular potentials essentially consist of periodically reoccurring population spikes. B, 25-trial averages of the FFT spectra of the extracellular potentials in A. Narrower population bursts increase power at both the oscillation frequency and its harmonics, with the power at the harmonics exceeding that at the oscillation frequency for very synchronous spiking. C, Average power spectra for 50–400 Hz rhythms in which the repeating Gaussian-shaped population bursts have widths of σ = 3, 2, 1 ms, independent of the oscillation. 6% of the population fires each 10 ms with spike times modulated within the periodic probability density function. Faster rhythms therefore have these spikes separated into more bursts and, consequently, have fewer spikes per burst.