Newsletter #253

Hey friends, this week I'd like to talk about one of the most under-appreciated sleep aids: masks. Like, the kind that you wear over your eyes.

First, let's talk about why they might be useful in the first place. Obviously, it's really tough to get deep restorative sleep when you're surrounded by a lot of external stimuli, like bright light or noise. If you stop and think about it from an evolutionary standpoint, that makes a ton of sense. In a natural environment, sounds or movement around us could signify potential danger. Consequently, most of us need the right conditions to fall asleep and stay asleep — quiet, comfortable, and free of stimulation.

That's where sleep masks enter the picture. They can help create those conditions by blocking out any light that might deliver an alerting signal to the brain. This is especially useful in the modern world, where light pollution can pervade at any time or place from artificial light sources.

Strangely enough, there have been very few studies that have actually examined the effects of sleep masks, and virtually none that look at masks in isolation. Most of this literature looks at the effects of eye masks (together with ear plugs) as a way to improve sleep in ICU patients. Sleep disturbances in intensive care units are basically the norm, for a number of reasons. One trial found that participants randomized to receive earplugs and masks increased their sleep by more than an hour, and also boosted the depth and continuity of that sleep.

But what about healthy folks? Well, a newly published trial suggests that wearing a sleep mask could not only improve the quality of your sleep, but also lead to a modest boost in performance the next day. Given that these masks are pretty much risk-free, and not terribly expensive, I was hyped to see this. It also caught my eye because of another recent study which suggested that we may be more sensitive to the brightness of ambient light than previously thought — even through closed eyelids. Scroll on down to learn more. 👀

Researchers from Osaka Metropolitan University in Japan recruited 33 students and conducted a series of experiments to measure light transmittance through their eyelids when their eyes were shut. Each participant sat on a chair in a dark room in front of a lighting device. First, they were exposed to a light of a particular color at a set brightness for one minute with their eyes closed, and were asked to try to memorize how bright it appeared to them. Then, at the instruction of the experimenter, they opened their eyes, and the subjects were asked to adjust the light intensity, using a hand-held remote controller, to match the brightness that they had experienced when their eyes were closed. The light sources used were monochromatic red, yellow, green, and blue LEDs, as well as a white LED. When the selected intensities were compared with the brightness of the light they had seen with their eyes open, it was determined that the average effective transmittance through their closed eyes was 52.4% for red light, 26.2% for yellow light, 21.6% for green light, 4.5% for blue light, and 42.7% for white light. These values are up to 10 times higher than eyelid transmittances reported previously. There were also significant differences between individuals, with some reporting much greater perception of brightness when their eyes were closed. Obviously, the experience of brightness being measured here is pretty subjective. But it does suggest that we might be more sensitive to ambient light when our eyes are closed than we thought — perhaps making a stronger case for ensuring a dark sleep environment.

Researchers affiliated with Cardiff University in Wales recruited 94 healthy young volunteers and had them wear a black eye mask every night while they slept for one week. At the end of the week, participants visited the lab and performed a series of cognitive tests. Then, one year later, researchers performed the exact same protocol again, except this time participants were equipped with eye masks with holes cut out over each eye, so that light was not blocked out at all. This is basically meant to control for any possible discomfort associated with wearing the mask. When the researchers compared the results on the cognitive battery, they found that when the subjects wore intact black eye masks, they performed better on a word-pair association task, wherein participants are shown a bunch of related word pairs (like river and boat for instance), and then are asked the next day to recall the associated words. They also had faster reaction times, compared to when they were wearing masks with holes. So, the masks appeared to be boosting memory encoding and alertness. But why? To gain insight into underlying mechanisms, the researchers recruited another group of 33 participants and basically replicated the experiment that I just described, except this time the subjects were equipped with special devices (Dreem headbands) that record brainwaves and thus can be used to estimate sleep staging. Again, they found that sleeping with the masks improved memory and alertness the following day. Data from the EEG headbands revealed that subjects got the same amount of sleep, regardless of whether they were wearing the masks or not. However, improvements in cognition from the masks were predicted by time spent in slow-wave sleep, also known as deep sleep. It's been known for some time that although we need an adequate amount of sleep for memory encoding, the quality of that sleep is also super important. For example, when researchers mildly disrupt sleep in a way that selectively suppresses slow-wave sleep but doesn't reduce the total amount of sleep, subjects show impaired memory performance. If you would like to learn more about how to achieve greater amounts of deep sleep, check out our interview with Kristine Wilckens.

This week, our friends Josh and Tommy answered a listen-submitted question: Are hearing aids a good idea for brain health?

We’ve known for some time that hearing and cognition are closely linked. Back in 1968, researchers performed a series of experiments to try to tease out how compromised intelligibility affected learning and memory.

For example, they played literature passages to participants, who then answered questions about the content. When the subjects had to listen to some passages under auditory conditions designed to mimic hearing loss, along with some passages that were played through high fidelity, their recall for all of the content was significantly worse — even the segments that were easy to hear and understand.

As researchers summarize, “…increased difficulty of recognition of speech through noise may interfere with other activities, (conveniently termed “rehearsal”) which may be necessary to efficiently retain data in memory.”

Since then, this phenomenon has become evident in recent epidemiological research, showing that hearing loss is associated with subsequent cognitive decline. A 2020 report of the Lancet Commission identified hearing impairment as one of 12 key modifiable risk factors for dementia.

But does this mean that you should go ahead and get a hearing aid as soon as you start to observe issues, to ensure that your senses are unencumbered? Or is that device effectively acting as a “crutch,” fueling further deterioration of function? Check out the pod to hear what Drs. Josh and Tommy think. Oh, and if you’d like to submit a question for the guys to tackle on the podcast, head on over to brainjo.academy/question.

This observation was first made more than a hundred years ago. Back in 1922, sociologists at Columbia University noticed that more deaths were recorded when the economy prospered. They thought at first that it must be a mistake, but further investigation confirmed that it was real. Since then, this finding has been replicated over and over again, around the globe and in different time periods, including after the Great Depression, as well as the Great Recession much more recently.

What is the explanation for this apparent paradox?

Well, there are a few possibilities. For one thing, people drive less, which leads to a reduction in car wrecks as well as air pollution. And when people spend less of their time working, they may get more sleep, more exercise, and experience occupational stress. Finally, even having less money can inadvertently lead to improved health by reducing consumption of drugs and rich foods and increasing reliance on home-cooked meals.

However, it is a little more complicated than that. Certainly, economic downturns also come with profound downsides, especially for vulnerable individuals, due to decreased healthcare access and a higher rate of "deaths of despair" (suicide and overdose).

According to public health specialist Harold Pollack: “Is a booming economy really good for people or bad for people? The answer, of course, is yes. What we have to do is understand the ways it is protective or harmful. And then determine how we can maximize the protective dimension and minimize the harmful.”

These masks have adjustable eye cups that mold to your face, blocking out light no matter how bright your surroundings. The cups are also deep, enough for you to open and blink your eyes, meaning no pressure on the lids. And most importantly, they're really comfortable, although it does take a little adjusting if you want to sleep on your stomach.

Fundamentally, the reason why masks work is they foster a dark environment. Melatonin is secreted by the pineal gland in response to darkness, and sends a circadian signal to help us fall asleep. This means that a mask can not only help you get quality sleep, but it can facilitate proper alignment of your circadian rhythm so that you sleep at the right time.But there is actually a plethora of things that we can do to optimize our body clock, and a lot of these activities actually occur during the day.

In this lesson, Dan explains the ideal way to engineer your light exposure patterns over a 24-hour period. For example, in addition to wearing an eye mask when you go to bed, you can also use glasses that block blue light in the hours before bedtime. Dan is an expert in sleep and circadian physiology, so you can rest assured that all of the recommendations here are based on solid scientific evidence.

And if you are looking for more personalized guidance, our upcoming coaching program may be a great fit for you.  If you haven’t already, I would encourage you to head to this link, and take 30 seconds to fill out the form so you’ll know when we’ve launched 🚀

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