The electroencephalogram of elderly subjects revisited.

The EEGs of 98 elderly volunteers were compared with those of 84 patients with a recent cerebral infarction who had achieved a stable clinical course. All subjects were uniformly evaluated according to a special protocol. The elderly volunteers were accepted for the study if they had no history, signs or symptoms of central nervous system disease. The EEGs were found to be significantly different between the two groups of subjects in several aspects. These included not only possible abnormalities, focal or diffuse, but also some normal features, such as alpha frequency and responses to photic stimulation and to hyperventilation. Groups of these differentiating features were analyzed. Using the single variable of ER (evoked response), discrimination of 80% was achieved. The variables that distinguish the volunteers from the patients may be used in the future to determine whether they are helpful in differentiating normals from patients with conditions other than stroke.