Is Nonlinearity Evident in Time Series of Brain Electrical Activity?

When we set out to apply nonlinear techniques, or even techniques inspired by chaos theory, to phenomena occurring in the brain, it seems wise to rst ask if the use of such advanced techniques is justiied by the data. While it seems very unlikely that the brain is a linear apparatus, its nonlinear nature might not be evident in speciic aspects of its dynamics and we might be better oo using the more familiar linear techniques. If we do nd nonlinearity, we still have to go a long way to understand its nature. I will show some cases of signiicant nonlinearity in time series none of which, however, shows deterministic chaos in any meaningful sense. The important question whether the observed irregularity is due to an intrinsic instability, the large number of neurons, or noise, may not be decidable based on time series data alone.