Waves that clear waste from the brain during sleep are impaired in older adults

As people age, they may experience shorter sleep durations and more frequent nighttime awakenings. A recent study from MIT researchers has revealed that a crucial process for clearing waste from the brain during sleep is often impaired in older adults. This process involves waves of cerebrospinal fluid (CSF) that remove debris from the brain.

The researchers discovered that these CSF waves are significantly reduced in older adults, and this impairment is not merely a result of getting less sleep. Instead, the slowdown appears to be linked to a decrease in the slow brain waves that typically occur during deep sleep. The study's senior author, Laura Lewis, suggests that understanding this connection could help predict future cognitive outcomes in individuals.

The researchers recruited participants from two age groups - 18 to 39 and 60 to 84 - and monitored their brain activity using functional magnetic resonance imaging (fMRI) and a specialized MRI technique that measures CSF flow. The study found that, during deep sleep, the slow waves were stronger and the CSF waves were larger in younger adults compared to older adults.

In older adults, the average CSF waves were significantly smaller, indicating a reduction in CSF flow. The researchers also explored possible factors contributing to this age-related decline in CSF flow. They found that reduced neurovascular coupling, where blood vessels fail to respond adequately to increased oxygen demand, and diminished blood flow were major factors in the reduced CSF flow.

However, they acknowledge that other age-related factors, such as vascular health and lifestyle, may also play a role. While none of the study participants had been diagnosed with neurodegenerative disorders, previous research has linked sleep disturbances to a higher risk of such conditions, including Alzheimer's disease.