Humans spend about one-third of their lives sleeping and even sleep-durations of humans are surprisingly short compared to other primates. We have known for a long time that sleep is restorative from personal experience and from research on cognitive functioning – learning, memory, reaction times, etc. (all of which suffers immensely from a night of missed sleep). But how exactly does sleep fix the brain?
In 2013 a group of researchers led by Lulu Xie and Hongyi Kang discovered that sleep is associated with a 60% increase in interstitial space (the space among neural cells), leading to increased exchange between cerebrospinal fluid and interstitial fluid (fluid that fills the space between neurons). This, they observed resulted in increased clearance of neurotoxins like amyloid-β peptides and tau proteins from the mouse brain. Accumulation of these neurotoxins is linked to neurodegenerative diseases like Alzheimer’s disease.
Now, a study by Per Kristian Eide et al. has investigated whether sleep deprivation affects the clearance of neurotoxins in the live human brain. The study compared the clearance of a tracer – MRI contrast agent Gadobutrol from the brains of participants divided into two groups. One group (N = 7) was totally deprived of sleep and the other (N = 17) was allowed to sleep freely for one night.
The tracer was injected into the spinal canal and found to have enriched brains of both groups similarly (“the study was restricted to patients under clinical work-up of tentative CSF disorders”). Imaging was done before the tracer was injected, after 0-1.5 h, 1.5–3 h, 4.5–7 h (Day 1), 24 h (Day 2), 48 h (Day 3), and after 4 weeks. Both groups were allowed to sleep freely starting day 2.
After just one night, there was significantly more of the tracer in the brains of the sleep-deprived group compared to the group that was allowed to sleep. The disparity persisted 24 hours and even 48 hours post-injection. A higher concentration of tracer was seen within the cerebral cortex and white matter.
The findings suggest that lack of sleep impedes clearance of neurotoxins from the brain and that it is not easy to compensate for lost sleep. Read more about the study here.
