Why do we need our eight hours sleep?
For decades, scientists have been baffled with this question, but now researches mayhave discovered what makes us fall asleep, why a long sleep feels good and why lack of it reduces our thinking power and can lead to dementia. People who have Alzheimer’s have been found to have an excess build up of beta-amyloid. This is a protein that clumps together and causes plaque in the brain and also in the blood vessels to the brain. Longer- term build up of amyloid are linked to Alzheimer’s disease. Hence, the process of eliminating these harmful toxins in the brain may reduce risk of Alzheimer’s. Researchers found that the conscious brain cannot spare the energy to eliminate the “toxic waste” it accumulates during the day and when the waste reaches a potentially damaging level, it triggers a powerful urge to sleep. During sleep the brain is able to reconfigure itself, opening up channels between its billions of cells and flushing them with cerebrospinal fluid. This clear colourless fluid from the brain bathes the brain and spinal cord. Besides being a transporter of nutrients and a filter of chemicals, it helps pad the brain as a shock absorber. Dr Maiken Nedergaard, a professor of neurosurgery at the University of Rochester believes that the flow of cerebrospinal fluid greatly increases during sleep. This flushes away damaging waste like the harmful protein beta-amyloid, which builds up while we are awake and alert. Dr Nedergaard said “one of the greatest mysteries in biology is why sleep is restorative and conversely, why lack of sleep impairs brain function. Sleep deprivation can reduce learning, impair cognitive performance, and is a common cause of seizures. In humans, fatal familial or sporadic insomnia is a progressively worsening state of sleeplessness. This can lead to dementia and death. The restorative function of sleep may be a result of the enhanced removal of potentially neurotoxin waste products that accumulate in the awake central nervous system”. The research was prompted by observations that concentrations of waste in the human
brain decrease during sleep and increase after waking. The same phenomenon was observed in mice. Dr Nedergaard understood this by studying mice and related this process to “a dishwasher”. Researchers injected dye into the cerebrospinal fluid of mice and watched it flow through their brains while simultaneously monitoring brain electrical activities. They found that the dye flowed rapidly when the mice were unconscious, either anaesthetised or asleep. However, the dye barely flowed when these mice were awake.
Dr Nedergaard said “we were surprised by how little flow there was into the brain when the mice were awake”. “It suggested that the space between brain cells changed greatly
between conscious and unconscious states”. By inserting electrodes into the brain to directly measure the space between cells, researchers found that the space between the
cells increased by 60 % when the mice were asleep or anaesthetised. Dr Nedergaard said“we need sleep”. It cleans up the brain
Dr Maiken Nedergaard told the American Association for the Advancement of Science annual meeting in San Jose “prior to this finding, no one really understood how the brain exports its waste”. It had been thought that the cells broke down and recycled their own waste.
Moreover, researchers found that waste flushing can become less efficient with age, providing insights into why the onset of dementia is associated with accumulation of toxic proteins.