4.3 Stages of Sleep

Stages of Sleep

Learning Objectives

  • By the end of this section, you will be able to:

    • Differentiate between REM (Rapid Eye Movement) and non-REM sleep.

    • Describe the differences between the four stages of non-REM sleep.

    • Understand the role that REM and non-REM sleep play in learning and memory.

Overview of Sleep

  • Sleep is composed of multiple different stages that are characterized by specific patterns of brain wave activity.

  • Brain Wave Patterns:

    • Visualized using EEG (electroencephalography).

    • Distinguished by frequency and amplitude.

  • Phases of Sleep:

    • Two general phases:

    • REM Sleep: Characterized by rapid eye movement and brain waves similar to wakefulness.

    • Non-REM (NREM) Sleep: Subdivided into four stages with distinct brain waves and characteristics.

Non-REM Sleep Stages

Stage 1 Sleep

  • Description:

    • Transitional phase between wakefulness and sleep.

    • Person drifts from being awake to asleep.

  • Physical Changes:

    • Decrease in respiration and heartbeat rates.

    • Reduction in overall muscle tension and core body temperature.

  • Brain Waves:

    • Characterized by alpha (8-13 Hz) and theta waves (4-7 Hz).

    • Alpha Waves: Seen at the onset, indicating relaxation.

    • Theta Waves: Increase as one continues into sleep.

  • Awakening:

    • Easily awakened; often reported as not having slept.

Stage 2 Sleep

  • Description:

    • State of deep relaxation.

  • Brain Waves:

    • Dominated by theta waves, punctuated by sleep spindles and K-complexes.

  • Sleep Spindles:

    • Rapid bursts of higher frequency brain waves, potentially important for learning and memory (Fogel & Smith, 2011; Poe et al., 2010).

  • K-complexes:

    • High amplitude brain wave patterns that may respond to environmental stimuli (Halász, 1993; Steriade & Amzica, 1998).

Stages 3 and 4 Sleep

  • Description:

    • Referred to as deep sleep or slow-wave sleep.

  • Brain Waves:

    • Characterized by delta waves (up to 4 Hz), low frequency, high amplitude.

  • Physical Changes:

    • Heart rate and respiration rates dramatically slow down.

  • Awakening:

    • Difficult to awaken someone; individuals awakened during this stage may feel groggy.

  • Notable Findings:

    • Increased alpha activity during these stages correlates with feelings of non-refreshment upon waking (Stone et al., 2008).

REM Sleep

  • Characteristics:

    • Marked by rapid eye movements and brain waves similar to wakefulness (Figure 4.12).

    • Associated with dreaming and muscle paralysis, except for crucial functions like circulation and respiration.

    • Known as paradoxical sleep due to high brain activity and lack of muscle tone.

  • Role in Learning and Memory:

    • Both NREM and REM sleep have been implicated in various learning and memory processes (Wagner et al., 2001).

    • Disagreement exists in the scientific community about the importance of NREM vs. REM for normal learning (Siegel, 2001).

  • REM Rebound:

    • If deprived of REM sleep, an individual will spend more time in REM during recovery sleep.

    • Suggests REM sleep is homeostatically regulated.

  • Emotional Processing:

    • REM sleep may aid emotional regulation, potentially decreasing emotional responses to aversive events (Suchecki et al., 2012).

    • REM deprivation could be beneficial for major depression, as some meds suppress REM sleep (Riemann et al., 2001; Vogel, 1975).

    • Alternative views exist on the effectiveness of non-REM sleep deprivation for mood improvement (Giedke & Schwärzler, 2002).

Dreams

  • Historical Perspectives:

    • Sigmund Freud: Dreams provide access to the unconscious mind.

    • Manifest Content: Actual storyline of the dream.

    • Latent Content: Hidden meaning behind the dream.

    • Example: Woman chased by a snake = fear of sexual intimacy (snake as a phallic symbol).

    • Carl Jung: Dreams tap into the collective unconscious, reflecting universal symbols and archetypes.

    • Rosalind Cartwright: Dreams reflect significant life events.

    • Empirical support where dream content correlated with women's thoughts of former spouses (Cartwright et al., 2006).

  • Technological Advancements:

    • Recent studies using fMRI have enabled researchers to classify visual images occurring during dreams (Horikawa et al., 2013).

  • Modern Theories of Dreaming:

    • Hobson (2009): Dreams create a virtual reality for problem-solving in waking life.

    • Lucid Dreams:

    • Defined as dreams where the dreamer is aware that they are dreaming and can control the content (LaBerge, 1990).