Ever wonder why you feel sluggish after a bad night’s sleep? Or why pulling an all-nighter makes it harder to focus, remember things, or even stay in a good mood? Sleep isn’t just a time for rest - it’s when your brain kicks into high gear, strengthening memories, clearing out toxins, and resetting for the day ahead. But what really happens while you sleep, and why is it so essential for peak brain function? Let’s unravel the mystery of sleep and discover why it’s the ultimate performance booster.
We often highlight the power of exercise and healthy eating, but quality sleep is just as crucial to unlock the best version of yourself. Sleep is not only essential for survival but it also plays an essential role in how your brain functions. As we take our night’s rest, our brain isn’t dormant - it performs multiple tasks that prepare us to tackle the next day. Let’s walk through the key things to understand about sleep and its profound impact on brain function.
Understanding circadian rhythm and the sleep cycle
In 1959, scientist Franz Halberg introduced the term ‘circadian’. The word itself is derived from Latin: circa meaning “about” and dies meaning “day.” But what exactly does it mean for us? Simply put, circadian rhythms are your body’s internal clock, regulating everything from your sleep-wake cycles to metabolism, hormone production, and even immune function (1,2).
In a 24-hour day, we experience two primary phases: wakefulness and sleep. Sleep itself is divided into two distinct stages - Rapid Eye Movement (REM) sleep and Non-Rapid Eye Movement (Non-REM) sleep.
During REM sleep, the brain is almost as active as it is during the day. Your eyes move rapidly in random patterns and your brain activity mirrors that of you being awake. Because of this intense brain activity, REM sleep is often referred to as paradoxical sleep - your body is at rest, but your brain is far from it.
In contrast, non-REM sleep is a more restful phase where brain activity slows down and your breathing becomes more regular. This stage is characterised by deeper relaxation, allowing your body to recover and recharge. The sleep cycle begins with non-REM sleep, followed by REM sleep, and continues to alternate between the two stages throughout the night. This cyclical process is essential for physical and mental restoration (3).
Before we move on, a quick fun fact - Dreams can occur in both REM and non-REM phases!
Sleep and Memory: The brain’s overnight backup system
Research over the years has established that sleep is crucial for memory consolidation. Memory consolidation is the process by which the brain transforms temporary memories into long-term memories (4).
Think of your brain as a sophisticated storage system. During sleep, it consolidates the day’s learning by transferring information from temporary, short-term storage to more stable, long-term memory - much like moving valuable data into a secure vault.
When you first learn something new, a part of your brain called the hippocampus is incredibly active. But with practice, the hippocampus 'calms down' while another area, the posterior parietal cortex, takes over to help store the memory long-term (5). Sleeping after learning new factual information significantly improves both the registration and retention of those memories, ensuring that they are more readily accessible later (6).
Sleep: The health hack you can’t ignore
Sleep deprivation disrupts immune function, triggering inflammation and increasing the risk of cardiovascular disease. It also leads to metabolic imbalances, affecting blood sugar regulation and contributing to fatigue and depression (7). Studies have also shown that sleep dysfunction plays a bidirectional role in pain conditions - poor sleep increases pain sensitivity and pain disrupts sleep. Sleep not only exacerbates pain, but may also aid in the development of chronic pain states (8,9).
Interestingly, not all parts of the brain transition through sleep stages at the same time. Research in rats suggests that the hippocampus enters REM sleep before other cortical networks, highlighting the complex and region-specific nature of sleep regulation. This early REM activation in the hippocampus could have important implications for memory processing, reinforcing the idea that different brain areas play distinct roles even while we sleep (10).
Brain detox 101: The Glymphatic system is at work!
Just like a computer that needs to clear out its ‘junk’ files, our brain produces waste daily and uses sleep as the ideal time to perform its 'clean-up'. During wakefulness, this system remains mostly inactive (11), allowing it to focus on cleaning while we rest. The brain's unique setup features ‘channels’ built by glial cells around blood vessels. These glial cells act as a dedicated ‘cleanup crew’ that efficiently removes toxins like amyloid-β - a substance linked to neurodegenerative disorders. Initially discovered in rodents, this glymphatic system has now been observed in humans thanks to advances in imaging techniques (12).
Caffeine: The Double-Edged Sword of Sleep and Alertness
We've all relied on coffee to get us through the day after pulling an all-nighter. While it may offer a temporary boost in alertness, it disrupts sleep and leads to daytime sleepiness, ultimately taking a toll on our sleep cycle (13).
In conclusion, quality sleep is not just a luxury - it is essential for your brain’s function, memory consolidation, and overall health. As much as we might think that we can compensate for a lack of sleep the next day, it is crucial to prioritise restful sleep to maintain peak cognitive performance and physical well-being. So, let’s make sleep a non-negotiable part of our routine, because it truly is the ultimate brain hack.
"If you're sleep-deprived, not even coffee can save you. You want to win? Get some sleep." A wannabe Harvey Specter
References:
1. Kuhlman, S. J., Craig, L. M. & Duffy, J. F. Introduction to Chronobiology. Cold Spring Harb. Perspect. Biol. 10, a033613 (2018).
2. Vitaterna, M. H., Takahashi, J. S. & Turek, F. W. Overview of Circadian Rhythms. Alcohol Res. Health 25, 85–93 (2001).
3. Tsunematsu, T. What are the neural mechanisms and physiological functions of dreams? Neurosci. Res. 189, 54–59 (2023).
4. Lee, J. W. & Jung, M. W. Memory consolidation from a reinforcement learning perspective. Front. Comput. Neurosci. 18, (2025).
5. Himmer, L., Schönauer, M., Heib, D. P. J., Schabus, M. & Gais, S. Rehearsal initiates systems memory consolidation, sleep makes it last. Sci. Adv. 5, eaav1695 (2019).
6. Cousins, J. N., Teo, T. B., Tan, Z. Y., Wong, K. F. & Chee, M. W. L. Sleep after learning aids the consolidation of factual knowledge, but not relearning. Sleep 44, zsaa210 (2021).
7. AlDabal, L. & BaHammam, A. S. Metabolic, Endocrine, and Immune Consequences of Sleep Deprivation. Open Respir. Med. J. 5, 31–43 (2011).
8. Haack, M., Simpson, N., Sethna, N., Kaur, S. & Mullington, J. Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications. Neuropsychopharmacology 45, 205–216 (2020).
9. Li, M. T., Robinson, C. L., Ruan, Q. Z., Surapaneni, S. & Southerland, W. The Influence of Sleep Disturbance on Chronic Pain. Curr. Pain Headache Rep. 26, 795–804 (2022).
10. Durán, E., Oyanedel, C. N., Niethard, N., Inostroza, M. & Born, J. Sleep stage dynamics in neocortex and hippocampus. Sleep 41, zsy060 (2018).
11. Jessen, N. A., Munk, A. S. F., Lundgaard, I. & Nedergaard, M. The Glymphatic System: A Beginner’s Guide. Neurochem. Res. 40, 2583–2599 (2015).
12. Iliff, J. J. et al. A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid β. Sci. Transl. Med. 4, 147ra111 (2012).
13. Roehrs, T. & Roth, T. Caffeine: Sleep and daytime sleepiness. Sleep Med. Rev. 12, 153–162 (2008).
This article was written by Vandana Shree Vedartham Srinivasan and edited by Rebecca Pope, with graphics produced by Lilly Green. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.
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