Wavelet Analysis of EEG signals

The wavelet transform (WT) has been used to study the nonstationary information in the Electroencephalograph (EEG) as an aid in determining the anesthetic depth. The Wavelet Transform (WT) provides an alternative to the classical Short-Time Fourier Transform or Gabor Transform. The reason for that is the self-adjusting window structure of the WT which results in a time-scale representation that displays the growth of the spectral components with varying resolutions. The WT will be briefly introduced, and its application in the analysis of transient nonstationary signals will be presented. The technique was utilized for the detection and spectral analysis of transient and background processes in the awake and asleep states. It can be observed that the response of both states before the application of the stimulus is similar in amplitude but not in spectral contents, which suggests a background activity of the brain. The brain reacts to the external stimulus in two different modes depending on the state of consciousness of the subject. In the case of awake state, there is a evident increase in response, while for the sleep state a reduction in this activity is observed. This analysis seems to suggest that the brain has an ongoing background process that monitors external stimulus in both the sleep and awake states.

Dr. Agostino Abbate

Last updated: 14 Feb 95