Do you sleep lightly or wake up feeling tired or groggy? Is getting the recommended seven to nine hours of sleep a night a challenge? If so, it’s likely you may not be getting enough deep sleep. 

Deep sleep plays a variety of important, restorative roles for the body and mind.  Without enough sleep and specifically, deep sleep, you increase your risk for a host of problems beyond daytime sleepiness including illness, mood swings, and memory issues.

If you’re wondering where deep sleep fits in the mix, it’s one of several sleep phases your brain cycles through each night while you are catching Zzz’s. If you ever had someone try to wake you up in the middle of the night and you didn’t budge in the slightest, you were probably in this stage of sleep.

During deep sleep, you do not dream, but it is still a very active and restorative sleep phase.  If you wake up during deep sleep, you will feel groggy and disoriented. Insufficient deep sleep is typically a side effect of getting too little sleep in general.  

Why is deep sleep important?

Deep sleep is a highly restorative phase of your nightly sleep patterns, both for your body and mind. During deep sleep, your breathing slows down and your heart rate is regular. Your body needs deep sleep in order to feel refreshed in the morning.  Without it, you will feel tired and groggy.  

Your body repairs its cells and tissues during deep sleep by secreting growth hormone from a region deep in the brain called the pituitary gland. This ensures that your wounds, muscle tissue, and your body’s cells will be restored and regenerated when you awake. That’s why it’s so important to get more sleep after major exercise or when your immune system is low.

But beyond the importance of deep sleep to boost daytime alertness and energy and repair your body, there are benefits for your brain cells as well.  Specifically, your brain cells use deep sleep as a time to recover and reset. Recent research has indicated that our brain uses cerebrospinal fluid to clear away toxins that build up during the day during deep sleep. When we’re getting consistently insufficient deep sleep, these toxic proteins can build up and contribute towards the development of diseases like Alzheimer’s. 

Memory consolidation also occurs during slow-wave sleep.  Without slow-wave sleep, your body and brain will not be able to function properly, resulting in poor memory performance and illness.

What is deep sleep? The science of deep sleep

There are four main stages of sleep, and you cycle through all of them each night in roughly ninety minutes. These stages include one REM (Rapid Eye Movement) sleep stage and three non-REM stages. Each sleep stage is associated with different neural activity.  Deep or slow-wave sleep is the last stage of non-REM sleep. Deep sleep is also referred to as delta sleep or N3 sleep. 

The brain is highly active during deep sleep

The brain cells located in the cortex — the largest part of the brain associated with higher brain functions such as thought and action — are involved in sleep.  Different sleep states are associated with different firing patterns in the cortex. Scientists were surprised to find that the brain cells in the cortex are active during slow-wave sleep, which was previously considered to be a state of rest for the brain.  In fact, research indicates brain cells of the neocortex can be even more active during slow-wave sleep than waking. 

Additionally, since our muscles aren’t entirely paralyzed during this stage of sleep like it is in REM sleep, certain sleep disorders are associated with it. This includes bedwetting, night terrors, and sleepwalking.

Deep sleep is a period of highly synchronous neural activity

Deep sleep is unique in that it is associated with the slowest, most synchronous brain waves during the nightly sleep cycle, which is why it is also called “slow wave sleep.”  

Your brain cells are active during slow-wave sleep and much less erratic compared to during wakefulness. Deep sleep produces slow brain waves called delta waves. These have a relatively high amplitude that occurs less than once per second. 

Scientists have compared this pattern of activity to an avalanche. The initial portion of each wave represents a short period of neuronal quieting when the brain cells in the neocortex are at rest — in other words, the brain cells are not actively firing in the first phase of the wave.  In the next phase of the wave, the brain cells fire rapidly for a very short period of time. This results in short bursts of brain activity during the deep sleep phase. Interestingly, these waves are regular and highly synchronous, so much so that you could predict the next one with the rhythm of the previous waves. 

You may wonder what your brain cells are doing firing so actively during this sleep phase.  Memory consolidation occurs during slow-wave sleep, and the neuronal firing bursts that occur during this phase may enable memories to be amplified and recalled until they are effectively stored.

How can I track my sleep to determine how much deep sleep I am getting?

You can use a sleep tracking app like Z’s sleep tracker to measure how much sleep you get each night.  If you want a more precise measurement of your sleep cycles, you might also consider a wearable sleep tracker. Here’s a list of wearables that are compatible with Z’s sleep tracker. 

If you’re getting a solid eight hours of sleep, then approximately 20-25% of the total sleep time should be deep, slow-wave sleep. This comes out to about 1.5-2 hours of deep sleep. 

When in the sleep cycle is deep sleep achieved?

Deep sleep can happen anywhere from 30 to 45 minutes after falling asleep. We tend to get most of our deep sleep earlier in the night, and then the balance shifts towards more REM sleep later on in the early morning. 

How can I get more deep sleep?

Here are a few evidence-based ways to get more deep sleep with lifestyle changes alone:

Actively reduce stress and listen to relaxing music before bed  

It’s easier said than done but stress is a leading cause of sleeplessness and can severely impact the quality of your nightly sleeping habits.  Yoga and meditation are two great ways to reduce stress and get deeper sleep. 

According to one study published in 2014, deep sleep can also be enhanced by listening to relaxing music one hour before bedtime. Try incorporating music like this relaxing sleep music into your nightly routine. Learn more.

Sleep more 

The best way to make sure that you get enough deep sleep is to sleep a minimum of eight hours a night.  Ensuring that you get enough sleep allows your brain to go through all of the different required phases of sleep — including slow-wave sleep — that leave you refreshed, repaired, and rejuvenated for the day ahead.  

Getting too little sleep is a surefire way of making sure that your body does not have time to go through all of the important sleep phases, which can cause a whole host of problems such as daytime sleepiness, memory issues, mood problems, and a lowered resistance to illness.

Engage in vigorous exercise regularly 

Physical activity such as running, jogging, and swimming can help you sleep better at night and increase the amount of time you spend in slow-wave sleep.  If you have trouble sleeping after a good workout, you may consider exercising earlier in the day rather than right before bedtime so as not to interrupt your sleep schedule. To learn more about the relationship between sleep and physical fitness, check out this article.

Avoid using your smartphone in bed.  

Smartphones emit blue light that can interfere with our circadian rhythms and disrupt our natural sleep schedules.  If you do read your phone at night, do so with your phone’s brightness set at the lowest setting to ensure that your mobile device’s backlight won’t interfere with your sleep. 

Maintaining good sleep hygiene habits will ensure that you get enough sleep overall, including slow-wave sleep.  Sleep has beneficial effects for immune and memory function as well as mood. So, next time you feel the urge to skimp on your sleep regimen, think about all the great benefits of a fully rested mind and body that you might be missing out on!

Glossary

Memory Consolidation: Process by which a temporary, fragile memory is restructured and transferred into a stable, long-lasting memory.

REM sleep: One of the two fundamental sleep states, along with NREM (Non-rapid eye movement) sleep. It is known as dream sleep, due to the presence of many dreams during this period. It is characterized by rapid eye movements, desynchronized brain waves, low muscle tone, and irregular breathing and heart rate compared to NREM sleep.

Delta wave: Neural oscillations in the 0.5Hz-4Hz range. They are associated with stages 3 and 4 of NREM (slow-wave sleep). 

Blue light – A type of visible light emitted by smartphone screens and backlights that can interfere with one’s sleeping patterns.

References

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  2. Bertha, Emily.  2018. The difference between REM and Deep Sleep.  Eight Sleep.  Accessible at https://site.eightsleep.cm/blogs/news/the-difference-between-rem-and-deep-sleep#.
  3. Cline, John.  2010. The mysterious benefits of deep sleep.  Psychology Today.  Accessible at https://www.psychologytoday.com/us/blog/sleepless-in-america/201010/the-mysterious-benefits-deep-sleep.
  4. Jones, B. 2016.  “Neuroscience: What are cortical neurons doing during sleep?” Current Biology, 26(21):R1147-R1150.  Accessible at https://www.sciencedirect.com/science/article/pii/S0960982216310776
  5. National Institute of Neurological Disorders and Stroke.  Brain Basics: Understanding Sleep. Accessible at https://www.ninds.nih.gov/Disorders/Patient-caregiver-Education/understanding-sleep
  6. Priesemann, V., et al.  2013. “Neuronal avalanches differ from wakefulness to deep sleep – evidence from intracranial depth recordings in humans.”  PLoS Computational Biology, (9)3:1-14.  Accessible at https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1002985
  7. Ribeiro, R, et al. 2004.  Long-lasting novelty-induced neuronal reverberation during slow-wave sleep in multiple forebrain areas. DOI: 10.1371/
  8. journal.pbio.0020024.  Accessible at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC314480/.
  9. Roth, Thomas.  2009. Slow Wave Sleep: Does It Matter?  Journal of Clinical Sleep Medicine.  Accessible at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824210/.
  10. University of Liège. "Human Brain Still Awake, Even During Deep Sleep." ScienceDaily. ScienceDaily, 17 October 2008. Accessible at https://www.sciencedaily.com/releases/2008/10/081008101740.htm