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Clin Neurophysiol. 2004 Mar;115(3):665-73.

EEG background activity described by a large computerized database.

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Department of Neurology, Section of Clinical Neurophysiology, Haukeland University Hospital, University of Bergen, 5021 Bergen, Norway.



To show how our newly developed software for classification and storage of visually routinely assessed EEGs are used to evaluate the general background activity (GBA) and the alpha rhythm (AR) in a large number of prospective EEGs.


EEGs from 4651 consecutive patients were visually assessed using a computerized description system connected to an EEG database. The AR and the GBA apart from the AR were described separately for frequency and amplitude.


AR frequencies declined from the age of 45 years and slowed with increasing age independently of non-AR pathology and gender. Females had higher AR frequencies than males. EEGs with non-GBA pathology had lower GBA frequencies and higher GBA amplitudes. Higher GBA amplitudes were associated with lower GBA frequencies in normal EEGs for all age groups. EEG interpretations by 4 independent electroencephalographers showed the same trends, but differed in exact assessment of frequencies and amplitudes.


EEG interpretations stored in a categorized database with easy access to data have successfully been used to evaluate interobserver variation and other quality control measurements. Statistical analysis of the data has at the same time produced new information regarding the development of AR and GBA throughout life.

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