Association of intracortical myelin and cognitive function in bipolar I disorder

Objective Although cognitive dysfunction persists through affective and euthymic states in bipolar disorder ( BD ), its neurobiological correlates remain undetermined. We explore whole‐cortex intracortical myelin ( ICM ) and cognition in BD ‐I and controls. Methods T 1 ‐weighted images (3T) optimized for ICM measurement were analyzed using a surface‐based approach. MRI signal was sampled at cortical mid‐depth. Cognitive performance was measured via standardized computerized battery and paper‐and‐pencil Trails B. Results ICM was associated with verbal memory ( VM ) in BD throughout a cortical network identified with pertinence to VM function, with strongest effects in left caudal middle temporal cortex and left dorsolateral prefrontal cortex ( P corrected  < 0.05). Subanalyses revealed specific association with correct word recognition, without delay. Processing speed, executive function, and reaction time were also predicted by ICM in BD , but not controls, although this did not survive Bonferroni correction. Conclusion This is the first study to show VM association with ICM in BD . ICM has been implicated in the integrity of neural connections and neural synchrony. VM dysfunction is one of the most replicated cognitive abnormalities in BD . Therefore, these results provide a novel mechanism for understanding cognitive dysfunction in BD , which can aid in the development of targeted therapeutics to improve cognitive outcomes in BD .