A Alvarez-Amador | PubMed Health

PubMed1988

A parametric model for multichannel EEG spectra.

The EEG is modelled as the superposition of two component processes: the xi and the alpha processes. In the frequency domain, the xi process is always present and appears as a spectral peak with maximum amplitude at very low frequencies, while the alpha process is characterized by a spectral peak with its maximum located in the traditional alpha 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 alpha is much larger than for xi, indicating increased functional coupling for the alpha process; (2) the alpha coherence matrix has reduced dimensionality, possibly related to a small number of generators; (3) xi coherences are zero phase with magnitudes that decrease exponentially with interelectrode distance; and (4) alpha coherences have significant nonzero phase shifts.

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[Spectral analysis of the electroencephalogram in children with systemic lupus erythematosus].

INTRODUCTION: Systemic lupus erythematosus (SLE) is an autoimmune disease that affects different systems and organs, including the central nervous system (CNS). It has been suggested that about 40% of the cases of neuropsychiatric lupus (NPSLE) develop before SLE is diagnosed or at the same time it is being carried out, and 63% appear during the first year following diagnosis. AIMS: The aim of this study was to check the hypothesis that the electroencephalogram (EEG) may be sensitive to the damage to the CNS in children with SLE in whom there is still no clinical evidence of NPSLE. PATIENTS AND METHODS: EEG recordings were performed in 30 children with a diagnosis of SLE with or without signs of a neuropsychiatric syndrome. The results of the EEG were evaluated visually and analysed quantitatively. RESULTS: The visual inspection of the EEG showed the presence of alterations in 44.5% of the children with SLE and in 76.9% of those with NPSLE. There were significant differences in Student's t test (p = 0.0055) between the two groups for the analysis of the broadband spectral measurements. The narrow band analysis revealed a significant increase in the theta and delta frequencies in children with SLE as compared to standard values, whereas in children with NPSLE significant differences were found in the fast bands in frontal regions. CONCLUSIONS: Spectral analysis of the narrow band could help to confirm diagnoses of NPSLE, while anomalies in the slow bands could be an early marker of damage to the CNS although there are still no symptoms of the disease.

Adolescent↗