Sleep Resets Neurons For New Memories The Next Day

While everyone knows that a good night's sleep restores energy, a new Cornell University study finds it resets another vital function: memory.

Learning or experiencing new things activates neurons in the hippocampus, a region of the brain vital for memory. Later, while we sleep, those same neurons repeat the same pattern of activity, which is how the brain consolidates those memories that are then stored in a large area called the cortex. But how is it that we can keep learning new things for a lifetime without using up all of our neurons?

A new study, "A Hippocampal Circuit Mechanism to Balance Memory Reactivation During Sleep," published in Science, finds that at certain times during deep sleep, parts of the hippocampus go silent, allowing those neurons to reset.

"This mechanism could allow the brain to reuse the same resources, the same neurons, for new learning the next day," said Azahara Oliva, assistant professor of neurobiology and behaviour and the paper's corresponding author.

The hippocampus is divided into three regions: CA1, CA2 and CA3. CA1 and CA3 are involved in encoding time- and space-related memories and are well-studied; less is known about CA2, which the current study found generates the silencing and resetting of the hippocampus during sleep.

The researchers implanted electrodes in the hippocampi of mice, which allowed them to record neuronal activity during learning and sleep. In this way, they observed that during sleep, the neurons in the CA1 and CA3 areas reproduced the same neuronal patterns that developed during learning during the day. But the researchers wanted to know how the brain continues learning each day without overloading or running out of neurons.

"We realised there are other hippocampal states that happen during sleep where everything is silenced," Oliva said. "The CA1 and CA3 regions that had been very active were suddenly quiet. It's a reset of memory, and the middle region, CA2, generates this state."

Cells called pyramidal neurons are thought to be the active neurons that matter for functional purposes, such as learning. Another type of cell, called interneurons, has different subtypes. The researchers discovered that the brain has parallel circuits regulated by these two types of interneurons -- one that regulates memory, the other that allows for resetting of memories.

The researchers believe they now have the tools to boost memory by tinkering with the mechanisms of memory consolidation, which could be applied when memory function falters, such as in Alzheimer's disease. Importantly, they also have evidence for exploring ways to erase negative or traumatic memories, which may then help treat conditions such as post-traumatic stress disorder.

The result helps explain why all animals require sleep, not only to fix memories, but also to reset the brain and keep it working during waking hours. "We show that memory is a dynamic process," Oliva said.

The study was funded by the National Institutes of Health, a Sloan Fellowship, a Whitehall Research Grant, a Klingenstein-Simons Fellowship and a New Frontiers Grant.

Eight Sleep Tips That Actually Work

Sleep advice is rife with misinformation because we all sleep differently—evolution

programmed us that way. We dug through the science and spoke to researchers to

determine the best sleep tips.

Why it matters:

Improving poor sleep is magic for your health and performance.

People sleep differently for good evolutionary reasons. And that’s precisely why hyper-specific sleep advice often backfires. We read stuff that makes us

worry that our sleep isn’t perfect—and worrying keeps us up at night, hurting our sleep even more.

It’s a sleep death spiral.

As Dr. Jade Wu, the sleep researcher at Duke University Medical School, put it:

“Just as you don’t need to have a ‘perfect’ meal at every meal to maintain nutritional

health, you don’t need to have flawless sleep every night. In fact, sleep is designed to be

elastic because your body’s needs and the environment’s conditions are constantly changing.

Letting go of sleep perfectionism can take a lot of pressure off the moment when you aren’t falling asleep right away or when you wake up during the night.”

Ask Yourself Four Questions About Your Sleep

Harvard professor Daniel Lieberman developed this questionnaire. He created it based on a deep analysis of sleep research, particularly this famous paper on sleep.

Before you try to correct any sleep issues you think you have, Lieberman suggests you ask yourself the following questions:

1. Am I generally satisfied with my sleep?

2. Do I stay awake all day without dozing?

3. Do I spend less than thirty minutes awake at night?

4. Do I get between six and eight hours of sleep a night?

If you answered no to those four questions, these eight tips may help you start to solve what could be a legitimate issue.

1. Find your ideal sleep time and try to stick to it

You’ve probably heard of circadian rhythms. These are our “biological clocks.” But our clocks, surprisingly, don’t match the 24-hour rotation of the Earth. And they aren’t all the same. Some people’s circadian rhythms, or biological clocks, are less than 24 hours. Some are 25 hours. The average is 24.1 to 24.3 hours.

Scientists say that people with longer clocks tend to be night owls. People with shorter clocks tend to get sleepy earlier in the evening. And our clocks change over our lifetime: In our teens and twenties, we tend to be night owls, but as we age, the curve shifts, and we often become the “early to bed, early to rise” people.

Instead of fighting this, lean into it. Do this:

1. Figure out your sleep clock.

The Duke researcher Jade Wu told Forbes, “The easiest way to know your chronotype is to ask yourself, ‘If I were on vacation on a deserted island for a month, what time would I naturally want to go to sleep and wake up?’” I.e., if you get sleepy at 9 pm, it’s fine to go to sleep. If you aren’t sleepy at 9 pm, don’t force it. Forcing it backfires.

Jerry Siegel, a UCLA Center for Sleep Research scientist, told us, “The simplest approach, which often works, is to awaken at the same time every day.”

Why it works: Understanding your natural rhythms and waking at the same time allows your body to sort of “tell” you how much sleep it needs. In turn, you’ll become tired at the ideal time each night.

2. Don’t drink caffeine after noon.

Siegel told us this simple rule works wonders for his patients.

Caffeine “works'' by binding to the receptors in our brain that lead us to feel tired. It also has a half-life of anywhere from 2 to 5 hours. Half-life is an estimate of the amount of time it takes for the concentration of a drug in your body to be reduced by half.

What this means in a common, real-life scenario: A venti Starbucks drip coffee (“venti” is Starbucks for large) has 400 milligrams of caffeine. The Mayo Clinic suggests we all keep our caffeine consumption under 400 milligrams a day. Going above that level seems to make enough (but not all) people have side effects—insomnia, anxiety, and more—that they think it’s good general advice.

Hence, if you drink a venti Starbucks drip coffee at 3 pm, you’ll still have a significant amount of caffeine in your system when you go to bed. Two notes:

There is some nuance here. People can adapt to high levels of caffeine; some people are

more affected by caffeine than others, etc. But if you’re concerned with your sleep and

hammering caffeine in the afternoon, stop caffeinating before noon and see what happens.

Caffeine’s half-life more than doubles if you are pregnant, according to researchers in

Switzerland. This is one reason why women who become pregnant and continue their regular coffee consumption often report sleep problems during pregnancy. They think it’s the pregnancy, but it’s really that the same amount of caffeine they used to drink now stays in their system four times longer.

3. Try CBT instead of RX

Jerry Siegel, the famed sleep researcher: “It’s a major myth that sleeping pills help you. The extant evidence is that chronic use of sleeping pills shortens lifespan.”

Cognitive behavioural therapy (CBT) is a better approach.

CBT is so effective that most big medical boards—like the American College of Physicians, Sleep Foundation, V.A., and more—recommend CBT as the top treatment for insomnia. It works and has no side effects.

Here’s why it works: Imagine you wake up in the middle of the night. What happens? You

probably then worry that you won’t go back to sleep. And if you can’t fall back to sleep, you

worry your day tomorrow will be a mess. And if your day tomorrow is a mess, then … This is the sleep death spiral.

Poor sleep is often driven by our thoughts—by the sleep death spiral. CBT kills the sleep death spiral. It helps us identify and overhaul the “thoughts, feelings, and behaviours contributing to the symptoms of insomnia,” as the Sleep Foundation put it.

(CBT is) kind of like doing physical therapy, but for your sleep … It's very tailored to you. At the end, you are hopefully not only sleeping better, but you have such a good

relationship with your sleep that you can weather future changes and challenges.

Downsides of CBT: It involves a specialist.

Upsides: Sleep is worth it, and most people only need a handful of CBT sessions.

4. Mess with your room’s temperature

Sleeping in total darkness and silence doesn’t work for everyone. It can backfire for many people.

Temperature, on the other hand, does seem to alter sleep. Just as humans evolved to sleep in “bedlam,” as Harvard scientists put it, we also evolved to sleep outside.

In the outdoors, the temperature usually drops below what it was during the day. So we may be adapted to feel that falling temperatures are a cue to sleep. To prepare for this nightly cooling, most mammals “curl up” to get warm. This process—get warm as it gets cold—may still help us today.

If you’re struggling to sleep, try turning down your room’s temperature before you go to bed and see what happens. Don’t go too cold, though. One old study found that rooms that were too cold impacted sleep more than rooms that were too hot.

5. Distract yourself

You’re not weird if you wake up in the middle of the night. Even great sleepers wake up an average of about 12 times each night. We usually don’t remember most of these wakeups.

Problems arise when we wake up and then obsess about getting back to sleep. Again, this is the sleep death spiral.

If you only wake up for longer periods now and then, a quick fix is just to distract yourself.

“You don't want to dread the act of being awake during the night because there's nothing inherently wrong with that,” Dr Wu told Plain English. “Do something that takes up just enough of your attention that your mind doesn't go to anxious places (and) end up spiralling. It's almost like counting sheep isn't good enough, because that's too easy. Your mind will start spiralling anyway, if you're prone to worry … so do something enjoyable.”

You could listen to an audiobook or podcast. Or read. You can even watch a rerun of your favourite show (my wife often does that). Stop listening, reading, or watching once you start to nod off.

And if you’re stressed about the next day’s to-do list, Dr Trevor Kashey suggested, “Write down your stressors and the times you will address them,” he said. The Ziegernik Effect suggests we remember (and often obsess over) uncompleted tasks more than completed ones. Writing down the unfinished task and exactly when you’ll complete it can help you feel enough closure to fall back asleep.

6. Go outside during the day

Andrew Huberman has made the practice of getting 15 minutes of direct sun exposure within 90 minutes of waking up a certifiable **thing.** He’s done such a great job promoting the behaviour that it’s become a meme.

It’s excellent advice. It’s also very specific advice.

Dr Wu, who studies sleep, suggests that simply going outside at any time of day is likely equally beneficial.

“It doesn't necessarily have to be early in the day,” she said. “(Going outside) during the day is better than not. More sunlight during the day is better. And why is that? Because that tells our circadian rhythms when it's day and when it's night. And the less confused it is about the timing, the better quality sleep.”

But if you have other stuff to do in your first 90 minutes and don’t have 15 minutes to give, just go outside sometime.

7. Exercise—But Not Before Bed

Scientists aren't entirely sure how exercise improves sleep. But who cares? When analysts

at the Sleep Foundation looked at all the studies, they concluded:

“(People) who experience poor sleep are less active than those with healthy sleep cycles. In particular, people with certain sleep disorders are not as likely to exercise during the day. Adults with insomnia tend to be less active than those without insomnia.”

If you exercise, you’ll not only (probably) sleep better. You’ll also (definitely) reduce your risk of dying at any given moment, feel happier and more energetic, and more. Even hitting 8,000 steps a day can help.

The catch: You also don’t want to do intense exercise within four hours of going to bed. “Body temperature can remain elevated up to two hours post-workout, making it difficult to decrease core temperature and induce sleep,” explained the wise Trevor Kashey, PhD

8. Don’t drink or eat before bed

In short, alcohol and big meals before bed tend to mess up our sleep.

Researchers in the UK analysed the data on how alcohol impacts sleep and wrote, “At all dosages, alcohol causes a reduction in sleep onset latency, a more consolidated first half sleep and an increase in sleep disruption in the second half of sleep.”

The answer for most of you isn’t to cut alcohol altogether. It’s to make a rational choice about when you’re willing to give up a bit of sleep quality for a few drinks.

As for eating, my friend Peter Attia, author of Outlive, analysed the research, spoke to experts, and concluded it’s best not to eat three hours before bed.

Two reasons:

1. Your food hasn’t fully digested, and lying down impairs digestion. This means you’ll likely get acid reflux, which can disrupt your sleep.

2. Digestion raises your body temperature, which is at odds with falling asleep. Higher protein meals raise your temperature the most.

If you have to eat right before bed, it won’t kill you. Some of you may sleep well after eating. But it’s a good practice for most people.

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