Hilbert-huang Transform Used for Eeg Signal Analysis

The EEG signals are recorded between electrodes placed in standard positions on the scalp. They have a typical amplitude of 2-100 μV and a frequency spectrum from 0.1 ÷ 50 Hz. The potential at the scalp derives from electrical activity of large synchronized groups of neurons inside the brain. EEG activity in particular frequency bands is often correlated with particular cognitive states. There are many ways to approach the understanding of brainwaves but the analysis of electroencephalograms (EEG) continues to be a problem due to our limited understanding of the signal origin. It is hard to design an effective evaluation method for the recorded signals. The Hilbert-Huang Transform (HHT) is in the centre of this study. This procedure is giving a deep insight of timefrequency structure of time series. The HHT method is exemplified on EEG signals recorded by our NSRG-team. In this paper we emphasize the technical aspects of the procedure and not the biological significance of the results.