A critical role for spike synchrony in determining steep 1/f slopes in the setting of bursting EEG patterns

EEG signals are commonly analyzed in the frequency-domain. Analysis of the power spectrum commonly demonstrates a reproducible fall-off of high frequencies, sometimes referred to as the "1/f slope". The 1/f slope comes about from a linear fit of the power spectral density in log-log form and takes typical values between (minus) 0-4. This slope has been recently hypothesized to correlate with the ratio of excitatory to inhibitory synaptic weights. However, we demonstrate models of excitatory-inhibitory (E/I) balance only explain small values of 1/f slope ( 2), which have been reported under conditions of anesthesia. Using simulations of clustered spike pulses, we find that pulse widths on the order of 1-10 ms result in a transition to steep 1/f slopes between 3-4. This trend also holds when measuring the 1/f slope from a spiking recurrent network model in a synchronous regime. We conclude that steep 1/f slopes result from synchronous spiking in bulk microcircuit activity. This suggests interpretations of steep 1/f slopes should consider spike synchrony in addition to other factors like E/I balance.