Idiopathic hypersomnolence (IH) is a central hypersomnia characterised by pathological sleepiness and confusional arousal. Research into IH is in its infancy. Physiological mechanisms behind clinical manifestations are unclear. Additionally, symptoms are not unique to IH, but are shared with other conditions such as narcolepsy and obstructive sleep apnoea. Boucetta et al. (2017) investigated changes in cerebral blood flow (CBF) patterns seen in IH as compared to healthy controls.
The study details regional changes in CBF specific to IH. Diagnosis was confirmed in subjects by polysomnography (PSG), and multiple sleep latency test (MSLT). SPECT scans conducted during a thirty-minute period of wakefulness with eyes open revealed definitive alterations to CBF.
Significant alterations were seen in multiple regions. Decreased CBF to the medial prefontal and posterior cingulate cortices bilaterally, putamen, and the left cerebellum. Increases in CBF at the left inferior temporal, inferior occipital cortices, and the left amygdala. These changes were not seen in corresponding controls. Additionally, these changes had statistically significant correlations with severity of daytime hypersomnolence.
Research has highlighted a potential contributor to IH specific daytime somnolence – an endogenous GABAergic mechanisms enabling increased GABA neurotransmission; promoting a decrease in wakefulness – a factor that may be localised to the medial prefrontal cortex. This can be localised to the medial prefrontal cortex (PFC), perhaps causing the hypoperfusion seen in the region. In light of this research, the PFC might be considered a more significant regulator of ultradian rhythms.
References
Soufiane Boucetta, Jacques Montplaisir, Antonio Zadra, Francis Lachapelle, Jean-Paul Soucy, Paul Gravel, Thien Thanh Dang-Vu; Altered Regional Cerebral Blood Flow in Idiopathic Hypersomnia, Sleep, Volume 40, Issue 10, 1 October 2017, zsx140, https://doi-org.ezproxy.library.uq.edu.au/10.1093/sleep/zsx140
