You may have experienced a time where you have gone 2 days without sleep, your mind is not as coherent and it feels as though you are floating through a thick fog in a rocking armchair. Why do we need certain hours of sleep to function well? What happens to our brains when we fall asleep?
There are 4 stages in a sleep cycle. The first 3 stages are non-rapid eye movement (NREM) sleep and the 4th is rapid eye movement (REM) sleep. Stage 1 NREM is where you transition from wakefulness to sleep. Stage 2 NREM gets you into a light sleep. When you go to Stage 3 NREM, you enter deep sleep. Stage 4 REM is when dreams occur and your body is immobilized.
“Busy Brains“
What is fascinating is what happens to our brain as we transition through the different stages of NREM and REM sleep.
New neurons are formed in the brain during the REM stage. Research showed that sustained sleep interruption dramatically reduced cell growth in the hippocampus1, the region of the brain involved in learning and memory. It’s no wonder we develop “brain fog” and our learning capability is slowed down by as much as 40% when we lack sleep.
A process known as synaptic pruning occurs during the NREM3 stage of sleep. Think of how we weed our gardens by pruning away unwanted branches and leaves? This is what synaptic pruning does – metabolite waste is cleared out from our brain. A study has shown that waste products of neural metabolism include peptides such as amyloid beta (commonly associated with Alzheimer’s disease) gets removed during restorative sleep2.
How many hours of sleep?
Typically we go through 5 full cycles of NREM and REM sleep in a night. Each full sleep cycle is around 90-110 minutes. This means we need about 7-8.5 hours of sleep per night. Sleep cycles maybe interrupted due to health conditions, habits and age. People who face repeated sleep disruption are at higher risk of inflammation, pain, high blood pressure and heart disease. There are individuals who may need less sleep due to their genetic makeup. It is rare though for anyone to need less than 6 hours of sleep.
With age, there is a tendency towards earlier bed time and earlier wake time. Older adults (age 65-75 years) typically go to bed 1.07 hours earlier and wake up 1.33 hours earlier than younger adults3. Age-related changes in the circadian rhythm, increased sensitivity to light and reduction in ability to maintain sleep pressure may be contributing factors to why older people experience decreasing sleep efficiency.
That said, don’t fret if you find yourself facing sleeplessness. It is common to lose sleep when we feel anxious or stressed. There are some simple ways to help you prepare for sleep.
Read next article: Tips on Sleeping Better
Reference
1 Guzman-Marin et al (2008) Adult hippocampal neurogenesis is reduced by sleep fragmentation in the adult rat, Neuroscience, https://doi.org/10.1016/j.neuroscience.2007.05.030
2 Xie et al (2013) Sleep drives metabolite clearance from the adult brain, Science, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880190/
3 Duffy et al (1998) Later endogenous circadian temperature nadir relative to an earlier wake time in older people. American Journal of Physiology
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