grayscale photo of sleeping woman lying on bed

Non-REM and REM sleep – what happens?

REM is rapid eye movements within sleep, and it is the period in which most of our vivid dreams occur. It starts to happen around 90 minutes after we first fall asleep and involves a high amount of brain activity (Siegel, 2005). The stage in which our body slows down is called non-REM sleep and there are 5 stages of sleep altogether:

Stage 1

This is the lightest stage of sleep and usually lasts for around 10 minutes. Your heart rate slows and your muscles relax in this stage, and your brainwaves slow down. It is, however, still possible to be easily awoken in this stage, as your brain produces alpha waves that are of high frequency (Abeln et al., 2014).

Stage 2

This is still classed as a period of light sleep, but the muscles become more relaxed than before. Your body temperature now begins to drop and your eye movements stop. Here, the brain begins to make rapid brain waves called sleep spindles which are important in memory and learning. This stage lasts for around 20 minutes (Fogel and Smith, 2011).

Stage 3 and 4

At this point, it becomes hard to be woken up as your muscles relax fully and your heart rate slows even more. This is known as deep sleep, and within these stages, the brain waves slow down (Abeln et al., 2014). A common event that occurs within these stages is sleepwalking.

Stage 5

This is where your body reaches REM sleep, the deepest stage of sleep which causes almost paralysis to the muscles. If you experience sleep deprivation, you may undergo something called a REM rebound which is where your body tries to make up for the lost REM sleep that it has missed (Verma et al., 2001). This is also the stage where dreams are most present, and studies have shown that those woken from REM sleep are much more likely to recall their dreams compared to those woken from non-REM sleep (Purves et al., 2001).

These stages are cycled by your body through the night approximately 4 or 5 times, which is why it is important to get between 7 and 9 hours of sleep each night for the experience of a deep sleep which helps your body to recover through the night.

Siegel, J. M. (2005). REM sleep. Principles and practice of sleep medicine4, 120-135

Abeln, V., Kleinert, J., Strüder, H. K., & Schneider, S. (2014). Brainwave entrainment for better sleep and post-sleep state of young elite soccer players–A pilot studyEuropean journal of sport science, 14(5), 393-402

Fogel, S. M., & Smith, C. T. (2011). The function of the sleep spindle: a physiological index of intelligence and a mechanism for sleep-dependent memory consolidation. Neuroscience & Biobehavioral Reviews, 35(5), 1154-1165

Verma, A., Radtke, R. A., VanLandingham, K. E., King, J. H., & Husain, A. M. (2001). Slow wave sleep rebound and REM rebound following the first night of treatment with CPAP for sleep apnea: correlation with subjective improvement in sleep quality. Sleep medicine, 2(3), 215-223

Purves, D., Augustine, G. J., Fitzpatrick, D., Katz, L. C., LaMantia, A. S., McNamara, J. O., & Williams, S. M. (2001). Physiological changes in sleep states. Neuroscience. 2nd edn. Sunderland, MA: Sinauer Associates

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