Apathy-related Neurobehavioral Markers of Cognitive Decline in Old-age Bipolar Disorders: Proof-of-concept

The goal of this clinical trial is to identify reliable markers of apathy in elderly subjects with bipolar disorder, age between 70 and 85 years, in order to accurately identify subjects at high risk of progressing to dementia by measuring motor activity (actimetrics), recorded language and analysing brain changes (MRI). Actimetry is the measurement and recording of body movements using an actimeter. This device is worn on the wrist and contains sensors capable of measuring and recording all movements, including those of very low intensity. An automated speech analysis using artificial intelligence is used to detect low-intensity anomalies, and we want to test whether individual differences correspond to individual differences in brain anatomy and function. Researchers will compare elderly subjects with bipolar disorder and healthy volunteer, age between 70 and 85 years. Participants will be asked to: * Perform an MRI * Complete 3 cognitive tests: verbal memory, verbal fluency and an emotional storytelling task, in which you will be asked to describe a memory orally using positive, negative and neutral emotions. * wear an actimeter on your wrist for 4 days.