The Longitudinal Course of Intracortical Myelination and Cognitive Function in Bipolar Disorder

Bipolar disorder is a mental illness that severely hampers healthy living and work productivity and affects more than 2% of the Canadian population - or more than half a million people. It is associated with episodes of depression (e.g. low mood, sadness) and mania (e.g. agitation, impulsive behavior), interspersed with periods of relative symptom relief between depressive and manic episodes. But even when their mood symptoms are absent or minimal, 60% of individuals with bipolar disorder show problems with attention, concentration and memory (also called "cognitive dysfunction"). This means that the majority of sufferers are chronically impaired. However, the exact causes of these brain deficits in bipolar disorder are unknown and there are no proven treatments for cognitive dysfunction in this population. We seek to investigate for the first time whether a loss of a specific substance, called myelin, in the outer part of the brain (the cerebral cortex) accounts for poor brain function in bipolar disorder. To that end, we will combine magnetic resonance imaging (MRI) to examine myelin with clinical testing to assess brain function in 100 individuals with bipolar disorder and 100 individuals who have no mental illness. They will be recruited at five sites across Canada and followed for two years. Our project will probe the link between myelin loss and poor brain function, which could suggest an important mechanism to improve brain function in those with bipolar disorder. In turn, this could guide new interventions to ameliorate their difficulties with thinking, concentration and memory.