Everything you wanted to ask about EEG but were afraid to get the right answer

Abstract

We answer several important questions concerning EEG. We also shortly discuss importance of nonlinear methods of contemporary physics in EEG analysis. Basic definitions and explanation of fundamental concepts may be found in my previous publications in NBP.It is a magnificent feeling to recognize the unity of complex phenomena which appear to be things quite apart from the direct visible truth.Albert Einstein.

Figure 1

Fourier decomposition of a signal of frequency 12 Hz with the amplitude modulated with frequency 1 Hz (upper) results in two harmonic signals – one with frequency 11 Hz and another with frequency 13; the basic frequency 12 Hz completely disappears.

Figure 2

FFT applied to two similar – stationary (upper left, a.) and nonstationary (lower left, b.) signals gives dramatically different results (right, c. and d.), while application of Higuchi's algorithm gives quite similar values of average fractal dimension, D_f, of both signals. The stationary signal was composed of five harmonic waves of different frequencies, and then randomly chosen small segments were removed from that stationary signal, so forming a nonstationary signal that when decomposed using Fourier leads to a very 'rich' spectrum of frequencies. Routine artefacts’ correction in EEG-signals may lead to similar unreliable cases.