Normal EEG


Well-structured EEG with stable and symmetrical posterior basic rhythm > 8 Hz and <13 Hz dominant in the posterior regions. Such activity has medium amplitude (30 - 50 µV) and is reactive to eye opening. No slow activities or epileptic pattern are present

Normal-limit EEG


Instable or suppressed alpha rhythm frequently replaced by high prevalence of diffuse beta rhythm (corresponding to grade A of Parsons-Simith’s classification)

Mild signs of encephalopathy:


Low frequency alpha rhythm (8 Hz) disturbed by random waves in the theta range over both hemispheres (corresponding to grade B of Parsons-Simith’s classification)

Distinctive features of encephalopathy:


Background activity in the theta range, diffused over both hemispheres. Random appearance of high waves in the delta range (roughly corresponding to grade C of Parsons-Simith’s classification)

Signs of severe encephalopathy:


Severe disorganization of EEG activity without any normal element. Diffuse asynchronous theta and delta waves over both hemispheres with or without triphasic waves (roughly corresponding to grades D-E of Parsons-Simith’s classification)