Sleep continues to be of great interest to scientists as we look to discover why it is so important for human survival. Sleep is not an inactive state, rather it is a period of time when strengthening and rejuvenation takes place. We know it matters for our bodies to restore and regenerate, to grow muscle, repair tissue and to synthesise hormones. We also know sleep matters for our brains and for optimal cognitive functioning. It is required for storage of memories and lack of it impedes attention, decision making, reasoning and focus.
Some new research led by Danish Neuroscientist Dr Maiken Nedergaard and her colleagues at the University of Rochester Medical Centre have now started to unlock some of the mysteries around the mechanisms behind sleep benefits for the brain. She is interested in the glial cells – a group found uniquely in the brain – and their purpose, believing them to be part of what keeps the brain “healthy”.
Given the fact that brain tissue has a significantly higher energy demand than other human tissues Nedergaard’s team were interested in the lack of a lymphatic system in the brain and spinal cord to “drain away” excess molecules such as proteins. The lymphatic system plays a critical role in the human immune system enabling the disposal of waste to the liver – so why does this process not apply to the brain? Her team have found that cerebrospinal (CSF) fluid, a clear liquid surrounding the brain and spinal cord, moves through the brain along a series of channels – managed by the glial cells. It is as if the CSF acts as a “sink” for waste and the brain actually can export molecules to the liver. Rodent studies show that the glia are the start of a transport network that end up in the lymph nodes in the neck. The team have termed this process the glymphatic system.
The team reported that this glymphatic system helps remove a toxic protein called beta-amyloid from brain tissue and their most recent research shows that sleep helps to clear these proteins. This has a huge implication for a number of neurological conditions such as Alzheimer’s and other dementias as they are characterised by an accumulation of proteins. Dr Nedergaard also points out in the journal Science that medical teams should allow patients with traumatic brain injury to sleep and not to keep waking them up every 10 minutes to take vital measurements.
The glymphatic system paves the way for more understanding of brain health. And the message is, as Dr. Nedergaard says, “…we need sleep. It cleans up the brain.”
The work was funded in the USA by the National Institute of Health’s specialist group – The National Institute of Neurological Disorders and Stroke (NINDS).