4.3 Stages of Sleep

• Sleep is divided into several sleep stages.
  • These stages can be differentiated from one another due to their differences in brain activity patterns.
  • These changes can be measured via an EEG, and it can be visualized as a brain wave.
  • Brain waves can have frequency and amplitude.
• Sleep is divided into two general phases: REM sleep and non-REM sleep
  • REM stands for rapid eye movement.
  • This phase of sleep is described by the movements of the eyes under closed eyelids.

Stage 0: Wakefulness

• Brain wave activity is dominated by -waves.
  • It has the highest frequency () and lowest amplitude.
  • They tend to have the most variability

Stage 1: NREM Stage 1 Sleep

• A transitional phase from wakefulness to sleep.

• Respiration and heartbeats slow down

• Overall muscle tension and core body temperature decreases.

• Brain wave activity is associated with both -waves and -waves.

  • Early portion of stage 1 sleep begins with -wave activity.
    • associated with relaxed, awake, and less variability (synchronized) activity.
    • has lower frequency () and higher amplitude than -waves.
  • As an individual continues through stage 1 sleep, -waves begin to increase.
    • has lower frequency () and higher amplitude than -wave patterns.

• It is easy to wake someone from stage 1 sleep.

Stage 2: NREM Stage 2 Sleep

• The body goes into a state of deep relaxation.

• -waves still dominate the activity of the brain

• Brain activity is often interrupted by sleep spindles and K-complexes.

• Sleep Spindle

  • rapid bursts of high-frequency brain waves.
  • may be associated to learning and memory.

• K-complex

  • a high amplitude pattern of brain activity
  • may occur as a response to environmental stimuli

Stage 3: NREM Stage 3 Sleep

• often referred to as deep sleep or slow-wave sleep

• heart rate and respiration slow drastically

• characterized with low frequency (), high amplitude -waves

• individuals with high levels of -wave activity during stage 3 sleep often report that they do not feel refreshed upon waking, regardless of how long they slept.

Stage 4: REM Sleep

• Brain waves in this stage are similar to brain waves when a person is awake.

• A period of sleep where dreaming occurs.

• Muscle systems are paralyzed during this stage

  • Muscle groups that make respiration and circulation possible are an exception.
  • No movement of voluntary muscles occurs in this stage.

• REM sleep is homeostatically regulated.

  • This means that people will spend more time on REM sleep given a chance to sleep without disturbance
    • This is in order to replenish the lost time in REM

• REM sleep also plays a positive role in other processes such as:

  • ones related to learning and memory formation
  • involved in emotional processing and regulation
    • this is why REM sleep is essential in suppressing emotional salience of aversive events occurred during wakefulness

• Hypnogram

  • a diagram of sleep stages occurred during sleep
  • illustrates how an individual moves through various stages of sleep.