24 Jul Idiopathic Hypersomnia: the structural and functional changes of the default-mode network.
There has been more research behind the cause for idiopathic hypersomnia with this particular study, performed by Pomares et al. (2019), looking at brain structures and functional changes. The main characterization of idiopathic hypersomnia is excessive daytime sleepiness and having difficulty waking from sleep. This is different to narcolepsy where the excessive daytime sleepiness is experience along with cataplexy and rapid REM onset. Due to the involvement of the default-mode network (DMN) in alertness and sleep, the aim of this study was to investigate the structural and functional changes of this area in those diagnosed with idiopathic hypersomnia.
A total of 27 patients were included in the study, 12 with idiopathic hypersomnia (IH) and 15 with good sleeping conditions (GSC). Measures of their daytime sleepiness were collected prior to the study which involved MRI scans of each patient. Gray matter volume and cortical thickness were looked along with the structural covariance and resting state functional connectivity to determine structural differences within the brain and changes within the default-mode network between the two groups of participants.
Results showed that there was no significant difference in overall gray matter, white matter, or cerebro-spinal fluid between the groups. Participants with IH showed smaller inferior frontal gyrus, larger gray matter volume in the left middle occipital gyrus and right precuneus (both are associated with the posterior DMN). The voxel-wise regression showed a significant positive correlation between gray matter volume in the middle occipital gyrus and the precuneus and daytime sleepiness. Participants with IH also showed thicker precuneus while showing no other region with lower cortical thickness.
These results show the importance of default-mode network in alertness and sleepiness when comparing those with IH and those without. Participants with IH had lower functional connectivity at rest within the anterior DMN, functional connectivity was negatively correlated with daytime sleepiness, and had larger posterior DMN (increased gray matter and thicker precuneus) when compared to those with GSC. Interestingly, the differences in the DMN in those with IH are different from other sleep disorders (eg: cataplexy narcolepsy and chronic insomnia). In conclusion, this study showed very real neural biomarkers that are specific to idiopathic hypersomnolence.
To read the full study and view scans, click here: https://doi.org/10.1093/sleep/zsz156