Nonlinear mechanisms of cortical oscillations

Not only theoretical consideration but also analyses of MEG or EEG recordings prove the nonlinear character of cortical dynamics. For instance, an averaged local Lyapunov Exponents (ILE) have positive value that is characteristic for chaotic dynamics. Also a test for nonlinearity (or determinism)--so called surrogate data test distinguishes between original- and randomized-phase time-series proving that recorded signals are nonlinear. These facts are a very strong experimental evidence to support the hypothesis that brain oscillators are governed by the deterministic, nonlinear, low-dimensional dynamics. The experimental manifestations of nonlinear cortical oscillations in the healthy and pathologically altered human brain and their deterministic character seems to be an important step in the understanding brain dynamics in the language of nonlinear systems theory. Clinical application may use nonlinear measures (especially ILE, and PD2i) for classification of pathologies and rough localization of the functional disturbance in the brain.