Psychology

With its mental plumbing connotations, there’s more to “sleep hygiene” than meets the eye.

How a good night’s sleep helps to clear our brains of clutter.

In the lead-up to Kirihimete, my family made advent calendars for each other. The 15-year-old got a deck of cards or something card-related each day. Such things as fanning powder, which, if you haven’t heard of it, is a bit like talc. It can be used to absorb the oils that come off your hands and accumulate on cards as you use them. Who’d have thought? Yes, it goes everywhere.

Of course, the ideal is to open each day’s gift together and, as the adults in the house have jobs to go to, that would preferably be early-ish. To cut a long story short, the gift-opening conflicted with the 15-year-old’s sleep routine. Long after Mum and Dad had gone for the day, he slumbered on.

As annoying as this might have been, it was also entirely understandable – sleep/wake times shift backwards as adolescence advances, until most can’t easily fall asleep before 11pm. Since teens need between eight and 10 hours of sleep a night, that means expecting them to be up and about at 7am is optimistic, and 9am is more realistic. And that’s assuming they’re actually in the land of nod promptly at 11pm. The US National Sleep Foundation outlines research that suggests only one in seven teens get the amount of sleep they need. Good thing they don’t get grumpy …

The Sleep Foundation goes on to note a slew of consequences arising from teens’ lack of sleep, including impairment of learning and memory, grumpiness (oops), negative effects on diet and health (pimples) and exacerbated effects from drinking alcohol. The less sleep teens get, the more depressed they are. Sounds like a perfect storm, or a script for an 80s teen movie.

But why do we need sleep? It appears to serve multiple functions. We know quite a bit about the rhythm of sleep, and everyone knows about rapid eye movement, or REM, sleep. Our sleep cycles start at about 90 minutes in length, including a period of REM sleep. This is when we’re most likely to dream, and is accompanied by “low muscle tone” – important so that you don’t act out whatever is happening in your dreams. Dreams, we think, are important for processing and filing the events of the day and, in the case of unpleasant events, a way to relive and thence get through the unpleasantness.

Sleep is also associated with an increase in “interstertial fluid volume” – the fluid between tissue cells and blood vessels. Your brain, for example, is surrounded by cerebrospinal fluid. This stuff cushions your brain a little from the slings and arrows of outrageous fortune, but also transports nutrients around.

And interstitual fluid moves metabolic waste, such as surplus proteins and the by-products of chemical reactions to the body’s “recycling stations”. Effectively, it’s a plumbing system for cleaning out your cerebral hardware, and the pumps work extra hard at night when we’re asleep.

We’ve known there’s some kind of waste-flushing process for a while, but not how it works. Until recently, that is. A more complete story is that astroglial cells, a bit like a large organisation’s cleaners, come together into networks to transport the rubbish away to the lymph nodes.

In other words, sleep is when the janitors get to work, and without enough of it, the halls don’t get cleaned. Rubbish-strewn halls are inefficient and cause accidents. It’s a health and safety nightmare. More than that, although it’s a stretch to say lack of sleep might be implicated in neurodegenerative conditions such as Alzheimer’s, it probably isn’t a good thing – buildups of particular types of proteins are involved, after all.

So the term “sleep hygiene”, which describes setting the right behavioural and environmental conditions for healthy snoozing, turns out to have another meaning as well. Unless you want to be tripping over mental rubbish tomorrow, let the clean-up crew work.

The plumbing system for cleaning out your cerebral hardware works extra hard during sleep.