How sleep affects human brain clearance

Credit: Isabella and Zsa Fischer/Unsplash.

In a new study from the University of Oulu, researchers reveal how sleep affects the brain clearance process.

The results of the study may help understand the mechanisms behind many brain diseases.

Previous study has shown that the clearance of waste in the brain is the most active during sleep, when an increase in the so-called delta waves can be observed in the EEG, especially during deep sleep.

There are three types of pulsations involved in this brain clearance: cardiovascular brain pulsation produced by the arterial pulse, respiratory pulsation in the veins and cerebrospinal fluid-filled spaces, and slow pulsations in the arterial wall.

It was previously unknown how these various types of brain pulsations related to brain clearance change when a person sleeps.

In the current study, the team used fast functional magnetic resonance imaging (fMRI) to scan the brains of healthy subjects during sleep and in the awake state.

They found that as the participants slept, the vasomotor and respiratory pulsations in their brains intensified and became more stable.

Moreover, cardiovascular pulsations also intensified during sleep, but these changes were visible in smaller areas of the brain.

In the areas where the pulsations intensified, an increase in delta waves was also observed in the EEG, which is indicative of increased brain clearance.

The increase in respiratory pulsation was at its greatest in areas of the brain that we use a lot during the day. These areas include the visual cortex, auditory cortex, and sensorimotor cortex.

The clearance of these areas of the brain is what is needed the most during the night.

The study also reveals that the intensification of pulsation activity already begins during lighter sleep and that deep sleep may not be needed.

Sleep disorders are known to be associated with many common brain diseases, such as Alzheimer’s disease, but the actual cause and effect relationships are not yet known.

It has been shown that the deterioration of brain pulsations and clearance precedes the accumulation of a beta-amyloid in the brain, which is typical of Alzheimer’s disease.

According to Heta Helakari, the current study and the available functional magnetic resonance imaging open the way to new and more feasible brain research.

If you care about sleep, please read studies about sleep apnea linked to autoimmune diseases and why people with sleep apnea more likely to have high blood pressure.

For more information about sleep, please see recent studies about treatment that could reduce severity of sleep apnea by one third, and results showing this sleep problem may increase risk of sudden death, high blood pressure.

The study was conducted by Heta Helakari et al., and published in the Journal of Neuroscience.