Stages of sleep

• There are five different sleep stages, including REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. The five stages make one sleep cycle, which usually repeats every 90 to 110 minutes.
• • Stage 1 non-REM sleep marks the transition from wakefulness to sleep. This stage typically lasts less than 10 minutes and is marked by a slowing of your heartbeat, breathing, eye movements, and the relaxation of your muscles.
• • Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep, which lasts roughly 20 minutes. Stage two is characterized by further slowing of both the heartbeat and breathing and the brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles.
• • Formerly known as stages 3 and 4, stage 3 (N3) is the final stage of non-REM sleep. This is the deepest period of sleep and lasts 20 to 40 minutes. Your heartbeat and breathing slow to their lowest levels, and your muscles are so relaxed that it may be hard to awaken you.
• • Stage 5 REM sleep occurs 90 minutes after sleep onset and is a much deeper sleep than any of the three stages of non-REM sleep. REM sleep is defined by rapid eye movements and an almost complete paralysis of the body, and a tendency to dream.
• Non-REM sleep is marked by a reduction of physiological activity as bodily functions slow down. There are three phases of non-REM sleep, commonly referred to as N1, N2, and N3.

  • Purves found that during these stages, electrical activity in the brain slows, growth hormone secretion occurs, and there is a decrease in muscle activity, heart rate, respiration, and oxygen consumption.
  • It is regulated by many brain structures, especially the thalamus and cerebral cortex.
• REM sleep is marked by intense brain activity and is a much more active period of sleep than non-REM.

  • McCarley found it is regulated by the brainstem which is the region of the brain that connects the cerebrum with the spinal cord. It consists of the midbrain, medulla oblongata, and pons.
• Dement and Kelitman (1957) conducted a study on 33 participants. They made EEG recordings of their brain activity over a nights sleep and found that brain waves followed a cyclic pattern of activation, with bodily relaxation occurring during slow wave sleep and rapid eye movement during periods of high activation.

  In a second study with 9 participants, they were woken at different stages in their sleep cycle and reported dreaming more frequently when woken in the REM stage.
• Strengths of ultradian rhythms:

  • Flexibility of explanation - A study by Randy Gardener where he remained awake for 246 hours, experiencing numerous problems, such as blurred vision and disorganised speech, showed he still coped very well. After the experience he slept for 15 hours and over several nights, recovered 25% of his lost sleep. He recovered 70% in stage 4 and 50% in REM. These suggest a large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of the ultradian rhythm.
• Strengths of the ultradian rhythm:

  • Practical application - Allows us to develop our understanding of biological rhythms. Research by Freidman and Fisher into the BRAC shows that the sleep cycle is part of a continuum within circadian rhythms. This suggests the 90 minute rhythm is important in keeping the biological processes in unison.
• Limitations of the ultradian rhythm:

  • Culture bias - Many studies were conducted on Western American and British samples. Tynjala found variations of sleep patterns in 11-16 year olds in Switzerland had a 1 hour difference than those in Israel. An important contributing factor was the number of evenings spent outside home, meaning that adolescents went to sleep later and got up early. This suggests the ultradian rhythm is influenced by cultural practices (eg meal time and play times).
• Limitations of the ultradian rhythms:

  • Individual differences - Tucker found significant differences between participants in terms of duration of each stage, particularly stage 3 and 4. Some may not go through all stages, resulting in lucid dreaming (wakefulness to REM). This suggests theories may restrict our understanding of the ultradian rhythm, demonstrating the innate differences.