A Parametric Model for Multichannel EEG Spectra

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Abstract
The EEG is model ed as the superposition of two component processes: the ξ and the α processes. In the frequency domain, the ξ process is always present and appears as a spectral peak with maximum amplitude at very low frequencies, while the α process is characterized by a spectral peak with its maximum located in the traditional α band (7-13 Hz), and is not necessarily always present. The multivariate properties of EEG spectra are adequately modelled with frequency independent coherence matrices for each process. Multichannel EEG studies reveal interesting properties: (1) the generalized coherence for α is much larger than for ξ, indicating increased functional coupling for the α process; (2) the α coherence matrix has reduced dimensionality, possibly related to a small number of generators; (3) ξ coherences are zero phase with magnitudes that decrease exponentially with interelectrode distance; and (4) α coherences have significant nonzero phase shifts.

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