Power-Law Scaling in the Brain Surface Electric Potential

Kai J. Miller, Larry B. Sorensen, Jeffrey G. Ojemann, Marcel den Nijs, Olaf Sporns
2009 PLoS Computational Biology  
Recent studies have identified broadband phenomena in the electric potentials produced by the brain. We report the finding of power-law scaling in these signals using subdural electrocorticographic recordings from the surface of human cortex. The power spectral density (PSD) of the electric potential has the power-law form P(f )*Af {x from 80 to 500 Hz. This scaling index, x~4:0+0:1, is conserved across subjects, area in the cortex, and local neural activity levels. The shape of the PSD does
more » ... change with increases in local cortical activity, but the amplitude, A, increases. We observe a "knee" in the spectra at f 0^7 5Hz, implying the existence of a characteristic time scale t~(2pf 0 ) {1^2 {4ms. Below f 0 , we explore twopower-law forms of the PSD, and demonstrate that there are activity-related fluctuations in the amplitude of a power-law process lying beneath the a=b rhythms. Finally, we illustrate through simulation how, small-scale, simplified neuronal models could lead to these power-law observations. This suggests a new paradigm of non-oscillatory "asynchronous," scalefree, changes in cortical potentials, corresponding to changes in mean population-averaged firing rate, to complement the prevalent "synchronous" rhythm-based paradigm.
doi:10.1371/journal.pcbi.1000609 pmid:20019800 pmcid:PMC2787015 fatcat:d5zowwx7zfhr7mlei24aed2cxu