Over 350 million people worldwide suffer from depression, a third of whom are medication resistant. Seizure therapy remains the most effective treatment in depression, even when many treatments fail. The utility of seizure therapy is limited due to its cognitive side effects and stigma. The biological targets of seizure therapy remain unknown, hindering design of new treatments with comparable efficacy. Seizures impact the brains temporal dynamicity observed through electroencephalography. This dynamicity reflects richness of information processing across distributed brain networks subserving affective and cognitive processes. We investigated the hypothesis that seizure therapy impacts mood (depressive symptoms) and cognition by modulating brain temporal dynamicity. We obtained resting-state EEG from thirty-four patients (age=46.0±14.0, 21 females) receiving two types of seizure treatments—electroconvulsive therapy or magnetic seizure therapy. We employed multi-scale entropy to quantify the complexity of brains temporal dynamics before and after seizure therapy. We discovered that reduction of complexity in fine time scales underlined successful therapeutic response to both seizure treatments. Greater reduction in complexity of fine time scales in parieto-occipital and central brain regions was significantly linked with greater improvement in depressive symptoms. Greater increase in complexity of coarse time scales was associated with greater decline in cognition including the autobiographical memory. These findings were region- and time-scale specific. That is, change in complexity in occipital regions (e.g., O2 electrode or right occipital pole) at fine time-scales was only associated with change in depressive symptoms, and not change in cognition, and change in complexity in parieto-central regions (e.g., Pz electrode or intra and transparietal sulcus) at coarser time-scale was only associated with change in cognition, and not depressive symptoms. Finally, region
