S2E40. Going Back To Sleep

It was just 9 weeks ago that I posted a blog about sleep (S2E31. Sweet Dreams Are Made Of This) in which I described my lifetime relationship with sleeping and napping.

I thought I had said all I needed to say about sleep’s importance as one of the five pillars of preserving brain health, but The Universe seemed to have a different idea. All of a sudden my inbox and social media feeds were full of articles about sleep and sleep hygiene…and it wasn’t even National Sleep Awareness Week!

So I played along and watched a webcast of an interview with Matt Walker, Ph.D., a sleep scientist at the University of California-Berkeley (you can watch the 1-hour event here: youtube.com/watch?v=ZaxGiYyUcyI).

A lot of the information he presented was new to me, so I read his book Why We Sleep.

WOW…was I ever impressed! It was a real page-turner! He keeps his use of jargon and scientific terminology to a bare minimum and has a knack for selecting just the right analogies to make the research he details come to life. But it’s the content he covers that is truly mind-boggling. It was humbling to discover how little I knew about sleep.

Did you know that all creatures who live more than a day sleep? Including insects and worms?

Did you know that only one side of a dolphin’s brain sleeps at a time because it has to stay awake to surface and breathe?

Did you know that just one hour of lost sleep can significantly impair your cognitive abilities and possibly even kill you? Apart from all the laboratory studies that demonstrate this, we have an unintended real-life experiment that is run every year. It turns out that the day after daylight savings time goes into effect (and we lose an hour of sleep by turning our clocks forward), there is a spike in the number of fatal heart attacks and car accidents. Conversely, when we turn our clocks back in the fall (and gain an hour of sleep), there is a corresponding drop in heart attacks and traffic accidents. 

Fascinating!

Apart from fun facts to know-and-tell, the research he described was simply amazing. He would begin by asking what happens when we sleep, then progress to how it happens, and end up answering the ultimate question: why does it happen?

For the purposes of this blog, though, the meaty part of the book involves sleep’s effects on memory.

Dr. Walker explains that the hippocampus maintains traces of your experiences each day and then, during sleep, it empties itself by sending important information out to a variety of cortical areas where it is permanently stored in the form of memories. It’s kind of like downloading the contents of a thumb drive onto your hard drive and then erasing it from the thumb drive so it has its full capacity available for the next day. One stage of sleep is responsible for transmitting the data and a different stage of sleep takes on the task of cementing it in place by strengthening the synapses where the information is stored.

If your early sleep is disturbed enough, the information won’t be transmitted and you won’t remember much the next day. If your sleep later in the night is disturbed, the newly planted memory won’t be consolidated and you won’t remember much, either.

So if you want to be able to remember more about what happened today, you’ll need a good 7-9 hours of high-quality sleep tonight…and for the next couple of days, as well.

If you don’t get good early sleep, the hippocampus won’t empty out and it will have limited storage space available the next day. That’s part of the dullness you feel when you haven’t slept well and accounts for some of the difficulty you have learning new information that day.

Unfortunately, once we get into our 60s, our sleep patterns begin to change…and not for the better. We tend to sleep fewer hours and the quality of that sleep is compromised by more awakenings…all of which wreaks havoc on our memory, immune system, emotional reactivity and judgement. 

It also compromises the nightly cleansing of the day’s chemical detritus which includes beta amyloid and tau particles, the accumulation of which are associated with Alzheimer’s pathology.

The take-home message here is that it’s not true that we need less sleep as we age. We need the same amount of sleep that we needed when we were younger to allow all of these crucial processes to be executed every night. The problem is that we don’t get the sleep we need as often as we should.

Putting all this together, it’s no surprise that getting fewer than the recommended number of hours of sleep on a regular basis is a risk factor for dementia. The relationship is so strong that researchers are now exploring whether sleep patterns can be used to predict whether or not you will develop a dementia a few years down the road.

Dr. Walker ends the book with a listing of things you can do to maximize your chances of getting the sleep you need (spoiler alert: taking sleep medication is not one of them). Here’s a link where you can review them: https://www.nhlbi.nih.gov/files/docs/public/sleep/healthysleepfs.pdf

The one change I made after reading the book had to do with my computer usage. 

I’m usually on the computer right up until bedtime, but it turns out that that’s a terrible thing to do. You see, the LED screen of a computer emits strong light waves at the blue end of the spectrum. It is this wavelength of light that triggers your circadian rhythm which tells you when to wake up and when to go to sleep. 

By bathing myself in blue light late at night, I was telling my brain that it was still daytime and so it delayed sending out the signal to initiate the sleep cycle until after I turned off the computer and went to bed.

I thought about changing my end-of-day routine, but realized I’m pretty much addicted to my computer use. Fortunately, the people at Apple have provided a solution. There is a program built into their computers and phones that will change the color emitted by their screens in the evening, going from blue-white to a soft yellow-amber. Problem solved! The program is called ‘Night Shift’ and you can find it by clicking on the ‘Display’ icon in System Preferences or Settings.

Alternatively, you can buy glasses that block the harmful wavelengths.

I’ll close with one more snippet from the book:

So, you ask, why is it that our circadian rhythm is triggered by blue light and not by full-spectrum sunlight?

You might recall that we are descended from fish and their aquatic predecessors. The circadian rhythm was an adaptation that evolved while we were living in water. But water filters out the other wavelengths of natural light leaving only the blues and greens. Eons ago, then, our evolutionary ancestors lived in a world that oscillated from darkness to blue and back again. And that’s the light pattern that controls your circadian rhythm to this very day!

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