What happens in the brain at night — and why it matters

An interview with Svenja Brodt about sleep, dreams, and health
 

In this conversation, we delve into the nighttime processes in the brain. Svenja Brodt sheds light on the functions of the different sleep phases and the role of dreams. She also explains why a restful night's sleep is essential for our health and gives tips for better sleep.

On average, we spend nearly one-third of our lives sleeping. However, not all sleep is the same every night, we cycle through several different phases. Let’s start from the beginning: what happens when we go to bed?

When we fall asleep, our brain activity changes drastically. This can be observed directly in an electroencephalogram: brain waves, which are fast and small when we are awake, become slower and larger; the brain switches down a gear.

After a fairly long period of light sleep, we enter deep sleep. It is often said that this phase is particularly restful. What makes it so special?

During deep sleep, neurons work even more in unison, causing brain waves to slow down and increase in size even more. This is the phase in which the key regeneration processes occur.

It is also often said that the brain is “cleansed” during deep sleep.

That’s right. It has only been known for about ten years that metabolic waste is flushed out of the brain during sleep.  This includes disease-causing plaques, such as beta-amyloid, which are associated with Alzheimer’s disease. This process requires slow brain waves, which enable the waste products to be gradually removed.

Many people find the final phase of the cycle, REM sleep, particularly fascinating because it is when we experience intense dreams. During this phase, the brain is highly active and uses a lot of energy. Why does the body engage in this costly activity?

That's a difficult question! REM sleep is the least understood phase. The brain’s activity during REM is strikingly similar to that during wakeful states. Interestingly, we tend to remember the intense and emotive REM dreams particularly well. It has been hypothesized that these dreams serve to process emotional experiences.

Some claim that they never dream. Can that be true?

It's virtually impossible to tell if you're not dreaming or just can't recall it. What you remember depends heavily on the sleep phase in which you wake up: sometimes, the level of neurotransmitters differs so greatly from the waking state that memory is impaired.

Is there anything you can do to remember your dreams more often?

Yes, you can train yourself to do this. Ask yourself, right when you wake up, what was just going through your mind. You will recall dreams more frequently and with greater detail once this becomes a routine.

Your research group “Brain States for Plasticity” studies the role of sleep in memory formation, among other topics. How exactly does sleep help the brain store information?

For a long time, there were two competing theories on this subject; we now know that both have some merit. One of them states that sleep is an elimination process in which brain activity and the neural connections formed during the day are downregulated and only the most important ones remain. The other theory describes sleep as an active process. We can best understand it by thinking of dreams: sometimes, we relive the day’s events at night. This reactivation occurs not only during dreams, but also independently of them, thereby strengthening memories.

What happens if we consistently don’t get enough sleep?

Some old studies have examined how long people can go without sleep; the world record is about eleven days. Needless to say, no one would conduct such an experiment today. The most serious consequence of acute sleep deprivation is that neural activity does not decrease and regeneration does not occur. Neurons remain permanently overactive, which can lead to an epileptic seizure in the worst case.

It is often said that the quality of sleep is as important as the duration. But what does sleep quality mean, exactly?

Healthy sleep involves spending enough time in each phase: mainly deep sleep in the first half of the night and REM sleep in the second half. However, it is also crucial that your night’s rest is not interrupted. Fragmented sleep, which occurs more frequently in old age, significantly impairs sleep quality.

Do you have one easy-to-implement tip for better sleep?

It's quite simple: the only thing you should do in bed is sleep. This is the core principle of sleep hygiene. Specifically, this means not using the TV to help you fall asleep. And if you lie awake for a long time at night, it's better to get up and only go back to bed when you're sleepy again.