Nonlinear EEG Changes Associated with Clinical Improvement in Depressed Patients

Assuming that the depressive syndrome could be related to a cerebral dynamical disease, we attempted to describe in a longitudinal and quantitative manner the modifications of brain electrical activity during depressive episodes treatment. This study tested whether mood improvement during therapy (pharmacological treatment or electroconvulsive therapy) is related to concomitant modifications of brain dynamics. The evolution of brain activity and mood were measured, every two days during treatment for three depressed patients and over three weeks for a control subject. Complexity of brain electrical activity was computed for each site of recording (EEG with 31 electrodes), leading to maps of complexity; depressive mood modulations were quantified using a self-assessment scale. The results show a specific organization of depressed patients' brain dynamics compared to the control's dynamics. Moreover, covariations between nonlinear changes in brain dynamics and mood improvement are observed during the remission of depressive episodes.