Sleep and Dreaming

When I was in college, the most popular elective class was “Sleep and Dreaming” offered by the Psychology department. Unfortunately, I was never able to fit it into my schedule but many of my friends took it – word on the street was that it was a ‘low workload’ class. I’ve been interested in the subject for a long time for two reasons, though. I had insomnia problems for many years, although thankfully those seem to have gone away with age. And I think I’m a lucid dreamer.

Why We Sleep by the neuroscientist Matthew Walker is the most interesting book I’ve read thus far. It’s aimed at the general public but is chock-full of scientific information. Reading it gives you the strong impression that the author is pushing sleep as the panacea to all manner of problems, but he does try to back it up with evidence.

The book opens by describing the latest knowledge in the science of sleep. It’s still mysterious but scientists now know a lot more about the process. Your sleep and wakefulness is determined by your circadian rhythm, typically following close to a twenty-four-hour cycle. The rise and fall of melatonin follows this rhythm in concert. The second factor is sleep pressure, controlled by adenosine. This substance keeps rising in concentration until relieved by sleep, which ideally happens after sixteen hours of wakefulness. Optimally you should try to get seven to nine hours of sleep per night. I also learned that evolutionary, our bodies naturally hit a lull in the early afternoon after lunch around siesta time. I used to take afternoon naps back in my younger days because I would only get to sleep in the wee hours of the morning. It was a vicious cycle of sorts.

You might call me a night-person – personified by the owl. The owl’s opposite is the lark. My spouse is a morning person – the lark. Early on we realized that conversations on complex matters should not be initiated early in the morning or later in the evening. Over the years I’ve slowly tried to move my circadian rhythm from owl to lark. I’ve been successful thanks to the aging process. While the circadian clock shifts rapidly to owl-ness starting at puberty and peaking at college age adolescence, there is a slow move back to lark-ness over the next twenty years. (This is from a large-scale German study from a number of years back.)

The sleep cycle comes in roughly 90-minute blocks, and the typical good sleeper has five cycles per night. There are five stages in each cycle: Being awake, REM, NREM Stage 1, NREM Stage 2, and finally NREM Stages 3-4 also known as slow wave sleep. REM stands for Rapid Eye Movement, the only thing part of your body you can move – your system ‘paralyzes’ everything else during this stage. Dreaming happens during REM sleep. NREM, or non-REM, sleep is when you are zonked out and you don’t remember anything.

Why do we have these different sleep phases? Walker offers a theory: “the uneven back-and-forth interplay between NREM and REM sleep is necessary to elegantly remodel and update our neural circuits at night, and in doing so manage the finite storage space within the brain… [This] requires identifying which memories are fresh and salient, and which memories that currently exist are overlapping, redundant, or simply no longer relevant… deep NREM sleep, which predominates early in the night, is to do the work of weeding out and removing unnecessary neural connections. In contrast, the dreaming stage of REM sleep, which prevails later in the night, plays a role in strengthening these connections.”

In your first couple of sleep cycles, you quickly move to deep NREM (slow wave) sleep and spend most of your time in that state. However, in later cycles, the amount of NREM decreases while REM increases. In the last stage before waking up in the morning, your sleep is mostly REM – which is why your dreams often happen in this final stage, and sometimes you can still remember them upon waking up!

Walker spends a section describing the benefits of sleep for learning. Before learning, it “refreshes our ability to initially make new memories”. Yes, there are sleep studies to test this, and yes, they involve napping and then taking a learning test! This seems to be tied to stage 2 (lighter) NREM sleep, particularly with bursts of electrical activity known as ‘sleep spindles’. But there’s also a benefit of sleeping after learning. “Sleep protects newly acquired information, affording immunity against forgetting: an operation called consolidation.” Deep NREM sleep is helpful here. Pulling an all-nighter before the exam without getting any rest in between is a recipe for not doing so great – although it might be better than no studying whatsoever. My recommendation to students: Get at least half a night’s sleep, if you can’t get the preferred full night. The first half is where you get the most deep NREM sleep.

What’s REM good for? Walker points out that humans have more intense REM sleep compared to all other mammals. He posits REM sleep and dreaming as key to “(1) our degree of sociocultural complexity, and (2) our cognitive intelligence.” It turns out that “REM sleep exquisitely recalibrates and fine-tunes the emotional circuits of the human brain.” Secondly, it fuels creativity: “REM sleep helps construct vast associative networks of information within the brain.” And yes, they’ve done experiments to try to figure all this out. I highly recommend reading Walker’s book for details! Want to get smarter? Get enough sleep.

One interesting chapter discusses “changes in sleep across the life span”. Sleep looks different in utero, during childhood, adolescence, midlife and old age. At the end of the book, Walker very strongly encourages moving high school start times to later in the morning. If anything, it significantly decreases teenage driving mortality in the early morning when kids don’t get enough sleep. He also exhorts the medical profession to change their grueling hours. Mistakes get made when you don’t get enough sleep. There’s another interesting chapter about sleeping pills. Quick summary: Don’t take them. They do the wrong things. Longer, detailed version: Read the book.

In the chapter on dreaming, Walker posits an intriguing theory: “Perhaps it is not time that heals all wounds, but rather time spent in dream sleep… REM-sleep dreaming offers a form of overnight therapy… [taking] the painful sting out of difficult, even traumatic, emotional episodes you have experienced during the day… [there’s] an astonishing change in the chemical cocktail of your brain that takes place during REM sleep.” Walker describes a powerful research example where a drug used to treat high blood pressure in veterans turned out to alleviate PTSD – by suppressing noradrenaline in the brain. It also turns out that REM sleep helps in “reading expressions and emotions of faces” and why certain types of autism are correlated to sleep problems. Walker calls REM-sleep dreaming an “emotional tuner”.

There is a separate chapter on “Dream Creativity and Dream Control”, and I was pleased that for the latter there are a number of MRI studies confirming that some people can indeed control our dreams. I do occasionally have a wild creative dream or one where I design a back-of-the-envelope chemistry card game. Others have claimed that groundbreaking ideas come through dreams. But most of my dreams are quite mundane and a number of them involve food and eating. Dreaming of the smell of food doesn’t quite match the real thing! Oh well. At least I’m enjoying my yummy sleep.

P.S. And in celebration of Pi Day, here's an older post reviewing How to Bake Pi.