Objective: Some studies on schizophrenia showed an increased complexity in electroencephalography (EEG) whereas others detected a decreased complexity. Because this discrepancy might be due to the clinical features or complexity measures used, we employed two different complexity measures in a group of schizophrenics similar in illness duration (chronic) and symptom profile (residual). Methods: Right-handed chronic residual schizophrenic patients (10 male, 10 female) and age-and sex-matched 20 healthy controls were included in the study. Eyes-closed resting EEG series were measured through quantitative EEG band activities, the log energy entropy (LEE) values, and the Hurst exponents (HE) of EEG measurements were computed for each electrode site. Results: Significantly higher LEE values in the prefrontal, frontal, temporal and parietal locations were observed in schizophrenic patients compared with controls. HE values were significantly higher on the right frontal area in the schizophrenics. Patient group showed increased prefrontal, frontal and parietal delta activity, prefrontal, left temporal and right parietal theta activity and increased left temporal alpha activity. Discussion: In the present study, we found that chronic residual schizophrenia is associated with decreased complexity and increased smoothness in EEG. In addition, EEG of patients was characterized by obvious slowness at prefrontal and frontotemporal regions, dominantly. An integration of EEG complexity and frequency analysis can be proposed as an innovative tool in schizophrenia research.
Conclusion: We integrate our results to gain an insight into abnormalities in the brains of schizophrenic persons, from a wide range of perspectives such as complexity, smoothness, and frequency. Patients had a decreased complexity and increased smoothness, measured by LEE, and an increase in slow activity, measured by FFT analysis. The right hemisphere was found to be more regular than the left one in schizophrenics. Both complexity and frequency analysis indicated that the abnormalities most often originated in the prefrontal, frontotemporal and parietal regions. Future studies of larger sample sizes that will be conducted on the different subtypes of schizophrenia using different subclasses of antipsychotic medications will shed further light on the area.