The brain’s ‘rubbish removal’ is most active at night.
While we sleep our brain is collecting and removing metabolic waste – in fact, one of the main benefits of sleep is that it supports better brain health! A recent study has found that this ‘garbage removal’ involves the central glymphatic system and is regulated by our circadian rhythm.
The glymphatic system is the brain’s ‘garbage collection’ and ‘rubbish removal’ service. Analogous to the systemic lymphatic system, the glymphatic system removes waste products such as oxidised fats, denatured proteins, and metabolic by-products – all of which can be harmful if left in the central nervous system (CNS). There is substantial interest in the glymphatic system’s role in waste clearance as a build-up of waste products is linked to disorders such as Alzheimer’s disease and Parkinson’s disease.
In the 2019 study by Cai et al., researchers looked at specific brain areas in awake and sleeping animals and measured function of the glymphatic system at different times of the day. They found that waste clearance was most effective when the animals were sleeping. Further, the found that glymphatic system activity is highest during the dark phase of the diurnal cycle and may be linked to the release of neuro-regulatory hormones such as melatonin.
Brain images also identified region-specific differences in the glymphatic system process of waste clearing. Areas of highest activity were along the occipital cerebrum (in humans this is the part of the brain is home to the visual processing, object/face recognition, and memory formation centres); areas of lowest glymphatic activity were in the midbrain (in humans these parts of the brain are responsible for motor control, alertness and temperature control).
Whilst caution must always be applied when extrapolating animal research to humans, these findings are none the less interesting as they highlight another potential important benefit of sleep – that is: supporting brain ‘garbage collection’ and ‘rubbish removal’ by the glymphatic system. This research further emphasises the need to ensure you are getting adequate, good quality sleep in order to support neurological health long term.
Reference: Cai, X., Qiao, J., Kulkarni, P., Harding, I. C., Ebong, E., & Ferris, C. F. (2019). Imaging the effect of the circadian light–dark cycle on the glymphatic system in awake rats. Proceedings of the National Academy of Sciences, 117(1), 668–676. doi: 10.1073/pnas.1914017117
Weblink: https://www.pnas.org/content/117/1/668