Brain layer shapes sleep quality via orexin signal
An almost unknown layer of the cerebral cortex turns out to play a key role in regulating the sleep-wake cycle. New mouse experiments show that this layer also shapes how orexin, a substance that promotes wakefulness, exerts its effects.
The cerebral cortex (the outer part of the brain) is built in layers. The deepest and least studied layer is called layer 6b (L6b). This layer is in direct contact with orexin, a signalling molecule that drives the sleep-wake transition. Orexin deficiency is also the cause of narcolepsy, a severe sleep disorder.
What changed without that layer
In mice whose L6b neurons were selectively silenced, total sleep time barely changed. But the quality and rhythm of brain activity did. The researchers measured slower theta frequency (a type of brain wave at 6-9 Hz) during waking and REM sleep in these mice, and less total brain activity during deep sleep (NREM sleep). The study was published in the journal eLife.
The mice with silenced L6b also responded differently to orexin injection. Orexin increased wakefulness in both groups, but in mice without active L6b, subsequent brain activity during deep sleep was lower.
Relevance for sleep and ageing
Sleep quality deteriorates with age. NREM sleep structure changes, theta rhythm shifts, and orexin systems fall out of balance. Whether L6b dysfunction contributes to those age-related changes is a question this research opens without answering.
The study was conducted in mice. Direct translation to human sleep behaviour requires caution. However, it offers a new angle for research into sleep disturbances in neurodegenerative diseases, where the layered structure of the cortex is often affected.
Search terms to explore further: orexin sleep-wake regulation cortex | cortical layer 6b brain oscillations NREM | theta rhythm sleep quality ageing