The dimensional complexity of the EEG during cognitive tasks reflects the impaired information processing in schizophrenic patients

The aim of the present study was to investigate whether schizophrenic patients show a different change of the dimensional complexity of the EEG, as represented by the Grassberger-Procaccia correlation dimension D-2, under cognitive challenge compared to normal control subjects. With respect to results reported in the literature, it was expected that the complexity of the signal under cognitive challenge is higher in schizophrenic patients than in normal control subjects reflecting the impaired information processing abilities of the patients. Eighty-seven schizophrenic and 30 matched control subjects performed two different types of the continuous performance task. The results revealed differences between schizophrenic patients and control subjects for the performance as well as the complexity measures. Schizophrenic patients produced more omission errors than normal subjects did. For the EEG complexity measure no differences occurred under the baseline condition. In contrast, during the first minute under task conditions the control subjects showed a decrease of the dimension while no changes were found for the schizophrenic group. These results occurred for both types of the cognitive task but they reached clear significance only in one of them. The results are interpreted as reflecting the ability of normal subjects to adapt their information processing system to the cognitive challenge and to focus their attention on the task while schizophrenic subjects do not show this adaptation to the task. (C) 2000 Elsevier Science B.V. All rights reserved.