Comparison between the alpha pattern in normal subjects and in alpha pattern coma.

Alpha pattern coma (APC) is an uncommon clinical EEG pattern in comatose patients, most commonly in association with anoxic-ischemic encephalopathy after cardiac arrest. Despite the pattern's striking similarity to that of the normal awake EEG, there are theoretical and experimental reasons for believing that the two rhythms result from different processes. The analysis of quantitative differences in APC from normal rhythms requires computer analysis. Because most cases of this rare entity have been collected over the years on paper traces, computer analysis appears implausible. In a companion article, we describe a method to quantify sections of paper EEGs. We applied this method to EEGs of five APC patients and five normal controls and noted a significant difference in the coherence between the two hemispheres in the alpha range. This finding is in keeping with theoretical, experimental, and clinical observations suggesting that APC may result from significant thalamo-cortical disruption.