Grant: Project Grant

Narcolepsy is a disorder characterized by excessive sleepiness: patients fall asleep during the day without being able to resist the urge to sleep. Narcolepsy is often accompanied by sudden episodes of muscle weakness triggered by emotions and termed cataplexy. Research in the past decade demonstrated that daytime sleepiness in narcoleptic patients who present cataplexy is related to a lack of a substance in the brain called hypocretin. However, some patients with narcolepsy never experience episodes of cataplexy. Furthermore, other patients presenting daytime sleepiness and no cataplexy closely resemble narcoleptic patients, but they tend to sleep for longer durations during the night and during daytime naps, without feeling refreshed after naps. This disorder is called idiopathic hypersomnia. No consistent lack of hypocretin has been observed in narcolepsy without cataplexy and idiopathic hypersomnia, and the brain abnormalities responsible for sleepiness in these disorders are poorly understood. This lack of knowledge considerably limits the possibility of developing optimal treatments. In the absence of more effective interventions, many patients with idiopathic hypersomnia or narcolepsy are dramatically affected by severe daytime sleepiness, which causes threatening risks of accidents, and impairs productivity and quality of life. Our objective is to analyze complementary modalities of brain imaging in patients with narcolepsy and idiopathic hypersomnia. This will allow us to identify brain regions and networks that are affected by these disorders, and will thus help us clarify the distinct brain mechanisms of daytime sleepiness in these different conditions. Understanding the brain regions and networks responsible for the disruption of daytime functioning in narcolepsy and idiopathic hypersomnia will be critical for developing new treatments, which will target the brain mechanisms specifically involved in each of these disabling disorders.