Comparison of different methods of time shift measurement in EEG.

Digital signal processing techniques are often used for measurement of small time shifts between EEG signals. In our work we tested properties of linear cross-correlation and phase/coherence method. The last mentioned method was used in two versions. The first version used fast Fourier transform (FFT) algorithm and the second was based on autoregressive modeling with fixed or adaptive model order. Methods were compared on several testing signals mimicking real EEG signals. The accuracy index for each method was computed. Results showed that for long signal segments all methods bring comparably good results. Accuracy of FFT phase/coherence method significantly decreased when very short segments were used and also decreased with an increasing level of the additive noise. The best results were obtained with autoregressive version of phase/coherence. This method is more reliable and may be used with high accuracy even in very short signals segments and it is also resistant to additive noise.

Electroencephalographic correlates of paced breathing.

Multichannel EEG, respiration, blood pressure and ECG were recorded during paced breathing at five frequencies in 18 subjects in order to elucidate the effects of paced breathing on power changes in alpha, beta and theta bands, and on rhythmical variability of these parameters. Mean power in the beta band and low-frequency beta power variability (0.12-0.04 Hz) increased during paced breathing at frequencies of 0.25 and 0.20 Hz. The total variability of alpha power in the right parietal and occipital electrodes decreased during paced breathing at 0.1 Hz compared with initial rest. The results point to increased cortical excitability during paced breathing at eupnoeic frequencies and to diminished cortical sensitivity to desynchronizing influences during paced breathing at 0.1 Hz.