Some evidence has been presented in previous articles supporting the hypothesis that relevant relationships may occur between clinical symptoms of depression and complex EEG features investigated by means of a systemic structural analysis (SSA). The present paper deals with a closer analysis of the clinical-neurophysiological relationships in depressive syndromes. 22 untreated depressed patients of both sexes participated in the study. The patients were rated by means of the Cronholm and Ottosson Rating Scale for Depression (CORSD) at the time of the EEG investigation. Special computer programs were used to investigate the relationships between clinical symptoms and elementary EEG characteristics. It was found that symptoms comprised in the ‘anxiety-depression’ subscale of the CORSD were related to fast activity in the EEG, whereas symptoms comprised in the ‘retardation’ subscale showed signifìcant relationships with slow EEG activity. The implications of these findings are discussed in terms of excitatory and inhibitory processes in the CNS. Both these processes exhibit a high degree of structural complexity and integration.

The tendency to ''augment'' or to ''reduce'' the amplitude of the response to stimuli of increasing intensity is a matter of much interest in the neurophysiological, psychophysiological and psychiatric literature. According to their response, individuals have been divided so far into ''augmenters'' and ''reducers'', and different mechanisms beyond these types of response have been discussed. In most studies, however, the major emphasis has been laid upon ''reducing'', which has been regarded as deviance from the expected ''augmenting''. In the present article, a new theory referring to a two-directional adaptive switch mechanism for coping with incoming stimuli is presented together with some hypotheses which can be derived from such a general theory. In the following, evidence from experimental work is presented which supports the main theoretical principles, and also the hypothesis that both basic characteristics of the central nervous system and biochemical variables contribute to the determination of the individual augmenting/reducing response.

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Previous investigations from our laboratory have suggested a possible interhemispheric difference in brain functioning in relation to the severity of a depressive psychopathological process. The present study has been carried out to extend the previous fìndings to comprise a more detailed symptom analysis of the depressive syndrome, several EEG characteristics, and a new method of EEG analysis. 22 depressed patients, most of them previously untreated, participated in the study. The patients were rated by means of a highly reliable rating scale for depression, and an EEG record was obtained from each of them. Analysis of possible relationships among clinical symptoms and EEG characteristics from different parts of the brain showed a complex pattern, quite different for each symptom. First when a systemic structural analysis of the EEG was performed by means of a special computer program, differential EEG syndromes could be identifìed. Patients with a high level of anxiety-depression showed a more pronounced functional involvement of the left precentral region than less severely ill patients.