Quantitative electrophysiological characteristics and subtyping of schizophrenia.

Quantitative descriptors of resting electroencephalogram (EEG) (QEEG) and event-related potentials (QERP) to visual and auditory stimuli were obtained from normal subjects and 94 chronic schizophrenic patients on medication, 25 chronic schizophrenics off medication, and 15 schizophrenics with no history of medication. These schizophrenic groups showed a high incidence of neurometric features that were significantly deviant from normative values. Multivariate discriminant analysis using these features successfully separated the schizophrenic patients from normals with high accuracy in independent replication. The data from the medicated group were subjected to cluster analysis. Newly developed algorithms were used for objective selection of the most effective set of variables for clustering and the optimum number of clusters to be sought. Five clusters were obtained, containing roughly equivalent proportions of the sample with markedly different QEEG profiles. The whole sample was then classified into these clusters. Each cluster contained patients both on and off medication, but patients who had never been medicated were classified into only three of these clusters. No significant clinical or demographic differences were found between members of the five clusters; however, clear differences in QERP profiles were seen. These results are described in detail and possible physiological and pharmacological implications are discussed.