Nonlinear dynamics of electroencephalography study in schizophrenic patients

Background Few characteristic changes of linear electroencephalograph （EEG） have been reported in schizophrenia. The aim of the present study was to investigate the changes in temporal-spatial dimensional properties of EEG under different cognitive tasks in patients with schizophrenia. Methods EEG was recorded by using EEG-1518K system and mapping system （Nihon Kohden Tomioka Corporation, Japan） in 45 schizophrenic patients and 47 healthy adults （normal control, NC） under five states： eyes c~osed, eyes open, mental arithmetic test with eyes closed, memory test with eyes open, and number cancellation test. Correlation dimension （D2） and point-wise correlation dimension （PD2） were calculated for all EEG analyses. Results （1） There were no significant differences of D2 and PD2 between NC and schizophrenic patients under states of eyes open and closed. （2） Compared with NC, schizophrenic patients showed decreased performance of D2 in mental arithmetic test with eyes closed and number cancellation test （mental arithmetic test with eyes closed： Nc 5.9±0.6, Sch 3.0＋0.8; number cancellation test： Nc 6.0±0.6, Sch 4.4±0.7; P 〈0.05 or P 〈0.01）. （3） Schizophrenic patients also showed decrease performance of PD2 in mental arithmetic test with eyes closed, memory test with eyes open, and number cancellation test （mental arithmetic test with eyes closed： Nc 6.9±0.7, Sch 4.0±0.8; memory test with eyes open： Nc 6.6±0.8, Sch 5.0±0.9; number cancellation test： Nc 7.1±0.7, Sch 4.8±0.9; P 〈0.05 or P 〈0.01）. Conclusions Nonlinear dynamic analysis provided a new approach in clinical investigation of EEG signals. It was helpful to further understand the cerebral mechanism in schizophrenic cognitive process.