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

Area of Science:

• Neuroscience
• Sleep Medicine
• Brain Imaging

Background:

• Idiopathic hypersomnia (IH) is a sleep disorder marked by excessive daytime sleepiness.
• Unlike narcolepsy, IH lacks cataplexy and hypocretin deficiency, leaving its mechanisms unclear.
• The default-mode network (DMN) is implicated in alertness and sleep regulation.

Purpose of the Study:

• To investigate structural and functional alterations of the DMN in individuals with idiopathic hypersomnia.
• To explore the relationship between DMN modifications and the severity of daytime sleepiness in IH.

Main Methods:

• Multimodal magnetic resonance imaging (MRI) was used, including gray matter volume and cortical thickness analysis.
• Resting-state functional connectivity and structural covariance analyses were performed on the DMN.
• 12 participants with IH and 15 healthy controls were studied.

Main Results:

• Participants with IH exhibited increased gray matter volume and cortical thickness in the precuneus, a DMN hub.
• A positive correlation between left medial prefrontal cortex and precuneus cortical thickness was stronger in IH.
• Lower resting-state functional connectivity within the anterior DMN (medial prefrontal cortex) was observed in IH and correlated with sleepiness.

Conclusions:

• Idiopathic hypersomnia is associated with distinct structural and functional DMN differences.
• These DMN alterations correlate with the severity of daytime sleepiness in IH.
• DMN disruption likely contributes to IH symptoms, potentially involving compensatory structural changes.