DON’T LET ME KEEP YOU AWAKE…

Guru Magazine - - Body - Au­thor: Si­mon Makin

Prac­ti­cally ev­ery­thing that moves and breathes needs to sleep. But in a world in which it’s ‘sur­vival of the fittest’, sleep­ing doesn’t make much sense – if you don’t want to get eaten by a preda­tor, that is. There­fore, there must be a good rea­son why so many liv­ing things spend a good chunk of their lives snooz­ing. But the ex­act pur­pose be­hind what Edgar Al­lan Poe called “those lit­tle slices of death” has eluded sci­en­tists for decades. Many sleep ex­perts think that sleep­ing

strength­ens the mem­ory and slum­ber is a time when the day’s events are moved into ‘long term’ stor­age. That may be true, but judg­ing by the dev­as­tat­ing ef­fects sleep de­pri­va­tion can have on our men­tal abil­i­ties (see ‘Dy­ing to Sleep’ on page

32), there’s lit­tle doubt that we need a reg­u­lar dose of Zs to keep our emo­tions and our minds bal­anced. Ex­actly how sleep weaves its restora­tive magic has been some­thing of a mys­tery – but now

new re­search says that one of the main rea­sons we sleep is to phys­i­cally ‘clean’ the brain. Ev­ery bi­o­log­i­cal process – and ev­ery chem­i­cal re­ac­tion – in the body pro­duces by-prod­ucts. The brain is no ex­cep­tion: it churns out waste, such as dam­aged pro­teins. This waste needs to be cleared away or else it will cause dam­age. Un­til now, the only way we thought the brain did this was by break­ing down and re­cy­cling the waste within brain cells. Last year, how­ever, re­searchers led by Maiken Ned­er­gaard at the Univer­sity of Rochester Med­i­cal Cen­tre, New York, dis­cov­ered a com­pletely new

brain waste dis­posal sys­tem. They found it us­ing a cut­ting-edge imaging tech­nol­ogy called two-pho­ton mi­croscopy, which of­fers a new way to look in­side a liv­ing brain. Ned­er­gaard and her col­leagues in­jected a spe­cial dye into the brains of mice and, us­ing the mi­cro­scope tech­nique,

spot­ted a drainage sys­tem that pumps liq­uid (cere­brospinal fluid) through the brain. This flow of fluid seems to ‘wash away’ ac­cu­mu­lated waste be­fore emp­ty­ing the ‘dirty’ liq­uid out of the brain and into the blood, where the waste can ul­ti­mately be de­stroyed in the liver. Ned­er­gaard and col­leagues dubbed this the ‘glym­phatic sys­tem’ (due to its sim­i­lar­ity with another of the body’s waste re­moval sys­tems, the

lym­phatic sys­tem). The re­searchers also thought that be­cause this newly-dis­cov­ered glym­phatic sys­tem uses a lot of en­ergy, it should be less ac­tive while the brain is awake and busy. To test their idea, they com­pared awake and sleep­ing mice, and found that the glym­phatic sys­tem was ac­tu­ally ten times more ac­tive dur­ing sleep. They strongly sus­pect that this hap­pens be­cause the tiny chan­nels be­tween blood ves­sels and cells that the fluid flows through get wider dur­ing sleep, al­low­ing flu­ids to pass more freely and “take out the trash”.

A dream an­swer for Alzheimer’s?

Fi­nally, the re­searchers went a step fur­ther by in­ject­ing a toxic pro­tein that has been strongly linked with Alzheimer’s disease, called be­taamy­loid, into mice’s brains. They saw that this waste pro­tein was flushed from the mice’s brains twice as

quickly when the mice were asleep. This could be an ex­tremely im­por­tant dis­cov­ery be­cause al­most all neu­rode­gen­er­a­tive dis­eases (such as Alzheimer’s) are as­so­ci­ated with the build-up of waste prod­ucts. This re­search may there­fore help us un­der­stand how sleep aids the brain, and ul­ti­mately how we might treat th­ese con­di­tions. We can’t be cer­tain whether th­ese mouse re­sults will ap­ply for us, so the next step is to check whether the same things hap­pen in hu­man brains. By pure co­in­ci­dence, just days af­ter th­ese re­sults came to light, re­search was pub­lished which shows that older peo­ple who sleep poorly have higher lev­els of the harm­ful beta-amy­loid waste pro­tein in their brains, as mea­sured by PET scans. The re­searchers be­hind this work urge cau­tion, in­sist­ing that their

re­sults don’t prove that poor sleep causes Alzheimer’s (it could be the other way round, for ex­am­ple). Sleep is, how­ever, start­ing to look like an ex­tremely plau­si­ble fac­tor in the de­vel­op­ment of Alzheimer’s. So not only will plenty of sleep make you a hap­pier, more alert per­son this Christ­mas, it may also im­prove your long-term men­tal health. How many more rea­sons do you need to catch up on all those Zs th­ese hol­i­days?

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