What a New Sleep Study Suggests About Brain Waste Clearance and Aging
An MIT-led study reports that cerebrospinal fluid waves that help clear brain waste during deep sleep are smaller in older adults, partly tied to weaker slow brain waves and reduced blood vessel responsiveness. Whether this affects neurodegenerative disease risk remains unknown.
The core finding
An MIT-led research team reports that waves of cerebrospinal fluid (CSF), which help carry waste products out of the brain, are notably smaller in older adults during non-REM sleep than in younger adults. The work was published in Nature Aging, with Laura Lewis as senior author.
How the study was done
Volunteers aged 18 to 39 and 60 to 84 were scanned late at night using fMRI, a modified MRI method for tracking CSF flow, and EEG. Many participants fell asleep in the scanner, allowing comparisons between wakefulness and sleep.
What else the researchers observed
- In younger participants, slow EEG waves strengthened in non-REM sleep and CSF waves grew larger.
- Older participants, on average, showed significantly smaller CSF waves.
- Awake tests suggested two contributors: weaker brain-vessel responses to neural activity and smaller blood-flow increases during breath-holding.
- A statistical model indicated these factors explained much, but not all, of the decline.
What remains unknown
The study did not show that reduced CSF flow causes neurodegenerative disease. None of the participants had a diagnosed neurodegenerative disorder, though some older adults showed gray matter atrophy linked to larger CSF-flow declines. The researchers hope to follow participants and test whether interventions, including a noise-based approach tried only in younger adults so far, can alter CSF flow. Some older participants maintained CSF waves in the younger range, and the reasons are unclear.
