Quantitative electroencephalographic (QEEG) changes relating to dissociative experiences have only rarely been demonstrated and dissociative states were not quantified in those studies. The aim of this study was to explore concurrent associations between quantified
dissociative states and QEEG spectral parameters, in particular theta activity, in psychiatric patients. Fifty psychiatric patients completed the State Scale of Dissociation (SSD) immediately after a 15-minute EEG recording. The EEG was assessed by conventional clinical visual analysis, as well as by quantitative (QEEG) spectral analysis. Canonical
analysis was performed between the set of SSD subscale scores and these QEEG parameters: alpha-theta magnitude ratios, and relative as well as absolute theta magnitude obtained from right and left mid- to posterior-temporal and parieto-occipital derivations. The SSD
transferred well to the present data in terms of reliability and internal-criterion-related validity. The SSD and DES correlated significantly (r=0.73;p<0.001). Conventional EEG analysis identified 29 EEGs (58%) as abnormal. The main abnormality in 23 EEGs was slowing, maximal temporally in half of these cases. Canonical analyses confirmed a
statistically significant relationship between the dissociation variables (especially conversion and depersonalization symptoms) and the QEEG variables (especially relative theta magnitude in the temporal regions) (R=0.72; p=0.03 for SSD-QEEG and R=0.66; p=0.04 for
DES-QEEG). Quantified dissociative mental states are positively canonically associated with decreased temporal theta activity and increased alpha-theta ratios on QEEG in psychiatric patients with a high tendency to dissociate. The potential implications of the dissociation theta-alpha relationship for understanding normal attentional processes need to be studied further.