Power-Law Scaling in the Brain Surface Electric Potential e1000609

• Published in: PLoS computational biology Vol. 5; no. 12
• Main Authors: Miller, Kai J, Sorensen, Larry B, Ojemann, Jeffrey G, Nijs, Marcel den
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 01.12.2009
• Subjects: Behavior; Electrodes; Experiments; Fourier transforms; Noise; Rhythm
• ISSN: 1553-734X; 1553-7358
• DOI: 10.1371/journal.pcbi.1000609

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 from 80 to 500 Hz. This scaling index, , is conserved across subjects, area in the cortex, and local neural activity levels. The shape of the PSD does not change with increases in local cortical activity, but the amplitude, , increases. We observe a "knee" in the spectra at , implying the existence of a characteristic time scale . Below , we explore two-power-law forms of the PSD, and demonstrate that there are activity-related fluctuations in the amplitude of a power-law process lying beneath the 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," scale-free, changes in cortical potentials, corresponding to changes in mean population-averaged firing rate, to complement the prevalent "synchronous" rhythm-based paradigm.