Unravelling the Science of Sleep

By Lisa Keenan

Every night, we spend several hours in a state that appears quiet and restful, yet the brain is buzzing with activity. It appears uneventful and ordinary, yet the mind is abound with fantastical images, stories, and emotions.

Across an entire lifetime, the average person will have spent a total of 26 years asleep. What is perhaps even more interesting is that an additional 7 years are spent lying in bed just trying to fall asleep. That's a total of 33 years devoted to sleep!¹

What really happens when we fall asleep each night and why are scientists so interested in learning more about it?

What happens during sleep?

It might feel like a smooth journey from when we first drift off to sleep at night to when we wake up the next morning, but sleep is actually more like a rollercoaster, with ups and downs all throughout the night. These ups and downs occur in cycles, each lasting approximately 90 minutes, bringing us from light to deep sleep. Depending on how long we are asleep, we go through a number of these cycles each night. They appear to follow a clear pattern, with four consecutive stages per cycle. Take a look at our image below to find out more!

With advances in brain imaging technologies, scientists in Aarhus University in Denmark recently found that these sleep stages might be much more complex than previously thought.² This means that there are still lots of secrets to uncover about sleep!

What parts of the brain are involved in sleep?

If you read our earlier blog post ‘Introducing: Your Brain!’, you will remember that the brain is made up of many working parts, each carrying out important functions. Some key brain areas associated with sleep include the hypothalamus, thalamus, brain stem, pineal gland, basal forebrain, and amygdala. Each of these brain areas have different roles to play in each stage of sleep. For example, the hypothalamus contains the suprachiasmatic nucleus, which controls circadian rhythm.

The circadian rhythm: Your 24-hour body clock

Your brain has a built-in body clock working 24 hours a day. It naturally keeps track of daily cycles of sleeping and waking, but can also be influenced by light, temperature, eating patterns, and activity levels.

This circadian clock is in charge of a number of important chemicals that influence when we should be awake and when we should be asleep. Firstly, histamines are released during the day to keep us awake. A chemical called adenosine slowly builds up in the body throughout the day, eventually causing you to feel sleepy. Closer to bedtime, melatonin is released, which prepares your brain and body for sleep.

Asleep but awake: The sleeping superpower of dolphins and birds

Some animals have very peculiar sleep behaviours. Dolphins and other marine animals, for example, can engage in unihemispheric slow-wave sleep (USWS) – this means that half of the brain is asleep while the other half is fully awake. Why exactly they sleep in this manner is not fully understood, but scientists believe that keeping half of the brain awake allows these animals to stay alert to danger, maintain body temperature, and control breathing. Birds can also use USWS to sleep while simultaneously soaring through the air!³

How do you think life might look different for humans if we had this special ability?

Why is sleep so important?

Sleep is essential for everyone, but the reasons for this were a mystery until relatively recently. And even now, scientists are still working hard to uncover all of the secrets and mysteries attached to sleep. We now know that sleep carries out a number of functions. For example, it allows us to process new information, form and maintain memories, repair and restore the body, and conserve energy.

Sleep also allows neurons to reorganise themselves in the brain, clearing out waste and ensuring the brain is ready to work well throughout the day ahead.⁴ This means that a good night of sleep can help us think more clearly, pay better attention, and regulate emotions.

Image credit: Katherine Streeter for NPR. — *Image credit:* Katherine Streeter for NPR.

Over time, our pattern of sleep can impact how the brain develops and builds connections. For example, scientists are starting to uncover a link between sleep and the development of something called executive function. Executive function is often referred to as the brain’s ‘air traffic control system’ because it allows us to pay attention, plan ahead, solve problems, remember important information, and change plans when needed.⁵

Recently, research has found that infants who experience sleep problems are more likely to have some difficulties with executive function later in childhood.⁶ Here at the UCD Neuropsychology Lab, we are researching sleep in children already at-risk for executive function difficulties. You can read more about this here!

How screens disrupt your circadian rhythm

Screens from most phones, tablets, and computers emit blue light. When we use our devices close to bedtime, our internal body clocks mistake this light for it being a sign of daytime. This means that important chemicals are not released properly, making it harder to sleep. Some doctors and scientists recommend setting a screen curfew each night to improve sleep. A recent study found that when teenagers set a screen curfew at 9pm each night, they not only slept better, but they were also more alert during the day.⁷

Try it yourself!

Screen Curfew.png — To set a screen curfew, you might decide that you will turn off all screens an hour or two before getting ready for bed each night.
If this seems like too big of a change right now, why not start small with 15 minutes of no screen time before bed?

How else can you improve sleep?

Limiting screen time is just one of many tips associated with something known as sleep hygiene. Despite the term, sleep hygiene is not about having a shower or bath before going to bed each night! Sleep hygiene refers to lots of different tips and recommendations that improve sleep.

If you are interested in improving your sleep hygiene and learning more about the science of sleep, take a look at some of the resources below! Don’t forget to check back next week, when Clara will talk all about our motor skills and how the brain allows us to move!

References

OECD. (2009). Special focus: Measuring leisure in OECD countries. Paris: OECD Publishing.
Stevner, A. B. A., Vidaurre, D., Cabral, J., Rapuano, K., Nielsen, S. F. V., Tagliazucchi, E., . . . Kringelbach, M. L. (2019). Discovery of key whole-brain transitions and dynamics during human wakefulness and non-REM sleep. Nature Communications, 10(1), 1–14. https://doi.org/10.1038/s41467-019-08934-3
Rattenberg, N. C., Voirin, B., Cruz, S. M., Tisdale, R., Dell’Omo, G., Lipp, H., Wikelski, M., & Vyssotski, A. L. (2016). Evidence that birds sleep in mid-flight. Nature Communications, 7(12468), 1–9. https://doi.org/10.1038/ncomms12468
Cao, J., Herman, A. B., West, G. B., Poe, G., & Savage, V. M. (2019). Unraveling why we sleep: Quantitative analysis reveals abrupt transition from neural reorganization to repair in early development. BioRxiv, 827212. https://doi.org/10.1101/827212
Center on the Developing Child at Harvard University. (2011). Building the brain’s “air traffic control” system: How early experiences shape the development of executive function: Working paper no. 11. https://developingchild.harvard.edu/wp-content/uploads/2011/05/How-Early-Experiences-Shape-the-Development-of-Executive-Function.pdf
Taveras, E. M., Rifas-Shiman, S. L., Bub, K. L., Gillman, M. W., & Oken, E. (2017). Prospective study of insufficient sleep and neurobehavioral functioning among school-age children. Academic Pediatrics, 17(6), 625–632. https://doi.org/10.1016/j.acap.2017.02.001
Perrault, A., Bayer, L., Peuvrier, M., Afyouni, A., Ghisletta, P., Brockmann, C., . . . Sterpenich, V. (2019). Reducing the use of screen electronic devices in the evening is associated with improved sleep and daytime vigilance in adolescents. Sleep, 42(9), 1–10. https://doi.org/10.1093/sleep/zsz125