Extraction of clinical information from electroencephalographic background activity: the combined use of brain electrical activity mapping and intravenous sodium thiopental.

Traditional visual inspection of electroencephalographic (EEG) tracings and computer-assisted topographic mapping were compared in their abilities to detect and locate supratentorial lesions following intravenous sodium thiopental administration. Of the 13 subjects, 8 had atrophic and 5 had mass lesions, all defined by computed tomographic scan and 11 confirmed at operation. EEGs made before and after thiopental administration were evaluated separately from topographic maps of statistical difference between EEGs at multiple frequency ranges made before and after thiopental injection. Topographic mapping of statistical difference accurately detected all thirteen lesions, whereas EEG detected eight. In addition to demonstrating reduced beta production overlying structural abnormalities, topographic mapping revealed regionally augmented beta, especially over irritative lesions. Moreover, localization was possible with the topographic method after the first thiopental injection, whereas a second injection was required for EEG localization by visual inspection. Changes in slow (delta) activity were also useful in delineation of atrophic lesions, in which delta was usually augmented but occasionally regionally reduced. Multielectrode studies with topographic mapping appear essential in delineating cerebral abnormalities, because both slow and fast activities may be increased or reduced over such areas. The relative response of EEG background activity to thiopental at different frequencies may assist lesion characterization as well as localization.