Title : Macroscopic Models of Local Field Potentials and the Apparent 1/f Noise in Brain Activity
Authors : Claude Bedard and Alain Destexhe
Year : 2009
Journal : Biophysical Journal
Volume : 96
Pages : 2589–2603
The power spectrum of local field potentials (LFPs) has been reported to scale as the inverse of the frequency, but the origin of this 1/f noise is at present unclear. Macroscopic measurements in cortical tissue demonstrated that electric conduc- tivity (as well as permittivity) is frequency-dependent, while other measurements failed to evidence any dependence on frequency. In this article, we propose a model of the genesis of LFPs that accounts for the above data and contradictions. Starting from ?rst principles (Maxwell equations), we introduce a macroscopic formalism in which macroscopic measurements are natu- rally incorporated, and also examine different physical causes for the frequency dependence. We suggest that ionic diffusion primes over electric field effects, and is responsible for the frequency dependence. This explains the contradictory observations, and also reproduces the 1/f power spectral structure of LFPs, as well as more complex frequency scaling. Finally, we suggest a measurement method to reveal the frequency dependence of current propagation in biological tissue, and which could be used to directly test the predictions of this formalism.