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 patie nts show a different change of the dimensional complexity of the EEG, as re presented by the Grassberger-Procaccia correlation dimension D-2, under cog nitive challenge compared to normal control subjects. With respect to resul ts reported in the literature, it was expected that the complexity of the s ignal under cognitive challenge is higher in schizophrenic patients than in normal control subjects reflecting the impaired information processing abi lities of the patients. Eighty-seven schizophrenic and 30 matched control s ubjects performed two different types of the continuous performance task. T he results revealed differences between schizophrenic patients and control subjects for the performance as well as the complexity measures. Schizophre nic patients produced more omission errors than normal subjects did. For th e EEG complexity measure no differences occurred under the baseline conditi on. 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 cogn itive task but they reached clear significance only in one of them. The res ults 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.