| Cranial Electrotherapy Stimulation (CES) involves the application of microelectric pulses to the subject using two electrodes placed on the head behind the ears. The therapy has been approved by the Food and Drug Administration (FDA) for treatment of insomnia, depression, and stress reduction. The acquisition of EEG during the administration of CES has been difficult due to the noise introduced by the CES stimulus. Hence, extensive EEG signal analysis and interpretation during CES therapy has not yet been documented in the literature beyond simple qualitative observations. This research investigates techniques and procedures for acquiring and analyzing EEG signals during the application of CES. The potential field and the current density distributions are calculated when CES is applied to a four-zone concentric spherical model representing the brain, the cerebrospinal fluid, skull, and the scalp. The model is used to predict the level of CES current that can be expected to reach the brainstem. A side effect of CES, aliasing of the stimulus into the EEG signal, is eliminated by analog and digital filters. Adaptive digital notch filters on the unit circle are investigated for the elimination of stimulus noise. The designed adaptive LMS notch filter has coefficients which are interdependent. The relationships between the coefficients of the filter simplify the gradient estimation through new recursive expressions. In addition, a new method based on a combination of the classical Fourier transform and period-peak detection is investigated for estimating the frequency spectrum of the EEG. The signal is considered as a train of truncated sinusoidal functions. Each truncated sinusoidal function is limited by two successive local extrema (a peak and a valley). The Fourier transform of the truncated sinusoidal function is a Sinc function. The summation of these Sinc functions yields the frequency spectrum of the signal. Finally, EEG analysis is used to examine the CES effects in a group of ten volunteer normal subjects. The EEG data are collected in three different trials where one trial is a sham. The results indicate that the CES stimulus affects the alpha-theta rhythms of the EEG. |
