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Sleep. 2019 Jul 22. pii: zsz156. doi: 10.1093/sleep/zsz156. [Epub ahead of print]

Beyond sleepy: structural and functional changes of the default-mode network in idiopathic hypersomnia.

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Center for Studies in Behavioral Neurobiology and Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal, QC, Canada.
PERFORM Centre, Concordia University, Montreal, QC, Canada.
Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Montreal, Quebec, Canada.
Center for Advanced Research in Sleep Medicine, Hôpital du Sacré-Coeur de Montréal, Montreal, Quebec, Canada.
Interdisciplinary School of Health Science, University of Ottawa, Ottawa, ON, Canada.
Department of Psychiatry, Université de Montréal, Montreal, QC, Canada.
Memory and Aging Center, Department of Neurology, University of California San Francisco, San Francisco, CA, USA.
USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA.
Department of Neurosciences, Université de Montréal, Montreal, QC, Canada.


Idiopathic hypersomnia (IH) is characterized by excessive daytime sleepiness but, in contrast to narcolepsy, does not involve cataplexy, sleep-onset REM periods, or any consistent hypocretin-1 deficiency. The pathophysiological mechanisms of IH remain unclear. Because of the involvement of the default-mode network (DMN) in alertness and sleep, our aim was to investigate the structural and functional modifications of the DMN in IH. We conducted multimodal magnetic resonance imaging (MRI) in twelve participants with IH and fifteen good sleeper controls (mean age ±SD: 32 ±9.6 years, range 22-53 years, 9 males). Subjective and objective measures of daytime sleepiness were collected. Gray matter volume and cortical thickness were analysed to investigate brain structural differences between good sleepers and IH. Structural covariance and resting-state functional connectivity were analysed to investigate changes in the DMN. Participants with IH had greater volume and cortical thickness in the precuneus, a posterior hub of the DMN. Cortical thickness in the left medial prefrontal cortex was positively correlated with thickness of the precuneus, and the strength of this correlation was greater in IH. In contrast, functional connectivity at rest was lower within the anterior DMN (medial prefrontal cortex) in IH, and correlated with subjective daytime sleepiness. The present results show that IH is associated with structural and functional differences in the DMN, in proportion to the severity of daytime sleepiness, suggesting that a disruption of the DMN contributes to the clinical features of IH. Larger volume and thickness in this network might reflect compensatory changes to lower functional connectivity in IH.


Brain Imaging; Cortical Activation; Functional Brain Imaging; Narcolepsy; Neuroimaging; Sleep and the Brain


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