Cerebral asymmetry in bipolar disorders: A scoping review

Current brain stimulation protocols for patients with bipolar disorders propose brain stimulation according to a model of opposing cerebral dominance in mania and bipolar depression by stimulating the right or left dorsolateral prefrontal cortex during manic or depressive episodes, respectively. However, there is very little observational, rather than interventional, research on such opposing cerebral dominance. In fact, this is the first scoping review that summarizes resting-state and task- related functional cerebral asymmetries measured with brain imaging techniques in manic and depressive symptoms or episodes in patients with formal bipolar disorder diagnoses. In a three-step search process MEDLINE, Scopus, APA PsycInfo, Web of Science Core Collection, and BIOSIS Previews databases as well as reference lists of eligible studies were searched. Data from these studies were extracted with a charting table. Ten resting-state EEG and task-related fMRI studies met inclusion criteria. In line with brain stimulation protocols, mania relates to cerebral dominance in regions of the left frontal lobe, such as the left dorsolateral prefrontal cortex and dorsal anterior cingulate cortex. Bipolar depression relates to cerebral dominance in regions of the right frontal and temporal lobe, such as the right dorsolateral prefrontal cortex, orbitofrontal cortex and temporal pole. More observational research on cerebral asymmetries in mania and bipolar depression can advance brain stimulation protocols and potentially inform standard treatment protocols.