Not Just Any MRI – Age and Time Tick for Brain Cleansing System

Published on May 22, 2023

Imagine your brain as a bustling city, constantly buzzing with activity. But just like any busy city, it needs a reliable waste disposal system to keep things clean. In the human brain, this essential function is carried out by the glymphatic system, which clears away harmful waste products. Scientists wanted to know if the efficiency of this waste clearance system depends on age and the time of day. Using advanced MRI techniques, they measured the influx and efflux activities of the glymphatic system in healthy volunteers ranging from 21 to 75 years old. Surprisingly, they found that the glymphatic system works at its best in the mornings, regardless of age. And as we get older, our brains might struggle more to clear out waste effectively. This discrepancy in waste removal rates could be due to changes in blood flow and water channels in the brain. These findings provide valuable insights into how the brain ages and may help better understand neurodegenerative diseases. To dive deeper into the fascinating world of brain cleansing and its impact on health, follow the link below!

Advanced age, accompanied by impaired glymphatic function, is a key risk factor for many neurodegenerative diseases. To study age-related differences in the human glymphatic system, we measured the influx and efflux activities of the glymphatic system via two non-invasive diffusion magnetic resonance imaging (MRI) methods, ultra-long echo time and low-b diffusion tensor imaging (DTIlow–b) measuring the subarachnoid space (SAS) flow along the middle cerebral artery and DTI analysis along the perivascular space (DTI-ALPS) along medullary veins in 22 healthy volunteers (aged 21–75 years). We first evaluated the circadian rhythm dependence of the glymphatic activity by repeating the MRI measurements at five time points from 8:00 to 23:00 and found no time-of-day dependence in the awake state under the current sensitivity of MRI measurements. Further test–retest analysis demonstrated high repeatability of both diffusion MRI measurements, suggesting their reliability. Additionally, the influx rate of the glymphatic system was significantly higher in participants aged >45 years than in participants aged 21–38, while the efflux rate was significantly lower in those aged >45 years. The mismatched influx and efflux activities in the glymphatic system might be due to age-related changes in arterial pulsation and aquaporin-4 polarization.

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