Psychology (9685) | Psychology of sleep

Welcome to the Psychology of Sleep! (3.3.1)

Hello future psychologists! This chapter dives into something we spend about one-third of our lives doing: sleeping. It might sound simple, but sleep is one of the most complex biological processes governed by strict internal clocks and external cues.
Understanding the Psychology of Sleep is crucial because it connects biological systems (Unit 2) directly to behaviour and cognition (Unit 1 and 3). Get ready to learn why your body demands sleep and what happens when that demand is ignored!

Section 1: The Three Types of Biological Rhythms

Biological rhythms are cyclical changes in bodily functions and behaviour that repeat at specific intervals. We classify them based on their duration.

1. Circadian Rhythms

The most famous rhythm! Circadian rhythms operate on a cycle that lasts approximately 24 hours (a day).

Key Example: The sleep/wake cycle.
Other Examples: Body temperature regulation, and the release of hormones like cortisol (high in the morning) and melatonin (high at night).

Did you know? Even if you are put in total darkness, your internal circadian clock runs slightly longer than 24 hours (usually around 25 hours). This proves it's driven internally, but needs daily correction.

2. Infradian Rhythms

These rhythms cycle less frequently than once every 24 hours (i.e., longer than a day).

Key Example: The female menstrual cycle (approximately 28 days).
Other Examples: Seasonal Affective Disorder (SAD), which follows a yearly pattern as light levels change.

3. Ultradian Rhythms

These rhythms cycle more frequently than once every 24 hours (i.e., shorter than a day).

Mnemonic Trick: Think U for Under a day.

Key Example: The stages of sleep, which cycle every 90-100 minutes throughout the night.
Other Examples: Cycles of alertness, feeding patterns (appetite).

Section 2: Control of the Sleep/Wake Cycle

How does the body know when it is 24 hours and time to go to sleep? It relies on internal clocks and external cues.

Endogenous Pacemakers (EPs)

These are the internal biological clocks that control our rhythms. They are "inside" the body.

The most important EP is the Suprachiasmatic Nucleus (SCN), located in the hypothalamus of the brain.

The SCN: The Master Clock

• The SCN receives information directly from the optic nerve about light levels.
• It sends signals to the pineal gland, instructing it when to release the hormone melatonin.
• Melatonin induces sleepiness. When light levels are low (night), SCN activity drops, melatonin increases, and we feel tired.

Exogenous Zeitgebers (EZs)

These are the external cues from the environment that reset, or "entrain," our internal clocks.

The most powerful EZ is light (which is why the SCN is connected to the eyes).

Other EZs include: Social cues (meal times, work schedules), and noise/temperature.

Analogy: Think of the SCN (EP) as a wristwatch that needs to be manually set every day using the sun or a time signal (EZ). If you ignore the EZ, your watch will drift off time!

Section 3: Disruption of Biological Rhythms

When our EPs and EZs fall out of sync, we experience disruption. The syllabus requires us to know about two key disruptions:

1. Shift Work

Shift workers (e.g., night nurses, factory workers) are forced to sleep during the day when their EZ (light) tells them to be awake, and work at night when their EP tells them to sleep.

Effects:

• Chronic fatigue and reduced concentration (leading to accidents).
• Increased risk of heart disease and sleep disorders.
• The internal clock (SCN) struggles to adapt to the changing schedule, leading to desynchronisation.

2. Jet Lag

Jet lag occurs when you fly rapidly across several time zones.

The Process: Your external time (EZ) suddenly changes (e.g., you fly 8 hours east, so noon instantly becomes 8 pm). However, your internal clock (EP) is still on the old time.

Symptoms: Difficulty sleeping at the new appropriate time, fatigue, reduced cognitive function, and digestive problems.

Tip for Exams: Traveling East is usually worse than traveling West, as traveling East shortens the day, forcing the SCN to adjust backwards, which is harder for the biological system.

Section 4: The Nature of Sleep: NREM and REM

Sleep is not a uniform state; it is composed of two main types that cycle throughout the night (an ultradian rhythm).

Non-Rapid Eye Movement (NREM) Sleep

NREM sleep consists of stages that move from light sleep to deep sleep.

NREM Stages:

1. Stage 1: Light sleep, muscle twitching, easily roused.
2. Stage 2: Deeper sleep, heart rate slows, body temperature drops. Sleep spindles (brief bursts of brain activity) appear on EEG.
3. Stage 3 & 4 (often grouped as N3/Slow-Wave Sleep): Deep sleep. Characterised by large, slow delta waves on an EEG. This is the hardest stage to wake someone from. This stage is crucial for physical repair.

Rapid Eye Movement (REM) Sleep

After NREM Stage 4, we cycle back up to REM sleep.

Characteristics:

• Brain Activity: High, active, similar to being awake (often called 'paradoxical sleep').
• Eye Movement: Eyes dart rapidly beneath the eyelids.
• Muscle Tone: Body muscles are essentially paralysed (atonia) to prevent you from acting out your dreams.
• Dreaming: This is the stage most associated with vivid, emotional dreams.

The sleep cycle repeats roughly every 90 minutes. Early in the night, NREM deep sleep (S3/4) dominates. Later in the night, REM sleep periods get progressively longer.

Section 5: Functions of Sleep: Why We Need It

Why do we spend so much time sleeping? Psychologists offer three main explanations:

1. Evolutionary Explanations (Adaptive Theory)

This theory focuses on survival. Sleep evolved as an innate adaptive mechanism.

Core Idea: Animals sleep when they are most vulnerable or when activity would be pointless/dangerous.

• Conserving Energy: When food is scarce, sleeping reduces metabolism and conserves calories.
• Inactivity at Night: Humans and diurnal animals (active during the day) are not well-adapted to hunt or forage in the dark. Sleep keeps us safe and hidden from predators when we are most vulnerable.

Critique: This theory explains *when* we sleep, but not *why* we need to lose consciousness for such long periods. If sleep is just to hide, why not just sit still and stay alert?

2. Restoration Theory

Proposed by Oswald (1984), this theory suggests sleep is necessary to repair and regenerate the body and brain.

Physical Restoration (NREM):

• During deep NREM sleep, growth hormone is secreted, necessary for cell repair, muscle growth, and tissue healing.
• Energy stores (like glycogen) in the muscles are replenished.

Psychological Restoration (REM):

• REM sleep is seen as crucial for restoring neurotransmitter supplies and dealing with emotional stress or complex thought processes (brain 'housekeeping').
• Babies spend much more time in REM sleep than adults, suggesting it is vital for brain development.

3. Memory Consolidation

This theory focuses on the cognitive function of sleep: processing, strengthening, and storing new memories.

The Process: During sleep, especially NREM and REM, memories are reactivated and transferred from temporary storage (hippocampus) to long-term storage (cortex).

• NREM Sleep: Crucial for consolidating declarative memories (facts, names, events).
• REM Sleep: Essential for consolidating procedural memories (skills, such as playing a musical instrument or riding a bike).

Practical Connection: This is why "pulling an all-nighter" before an exam is often counterproductive—you prevent your brain from consolidating what you learned!

Section 6: Sleep Disorders

A sleep disorder is a persistent disturbance of normal sleep patterns that causes distress and impacts daily functioning.

1. Insomnia

Insomnia is the inability to fall asleep, stay asleep, or obtain a quality amount of sleep, despite having the opportunity to do so.

Insomnia and Personality/Genetics:

• Personality Factors: Individuals with certain personality types, particularly high levels of anxiety, worry, or perfectionism, are more prone to chronic insomnia. They may catastrophise the lack of sleep, making the problem worse (a cognitive explanation).
• Genetics: Research suggests a genetic predisposition to insomnia. Studies involving twins and families show that a vulnerability to chronic sleep problems can be inherited.

2. Narcolepsy

Narcolepsy is a neurological disorder characterised by the inability to regulate sleep/wake cycles normally, resulting in sudden, irresistible sleep attacks.

Key Features:

• Sudden Sleep Attacks: Uncontrollable urges to sleep, often at inappropriate times.
• Cataplexy: A sudden and temporary loss of muscle tone (collapse), often triggered by strong emotions like laughter or anger. This is essentially REM paralysis occurring when the person is awake.
• Cause: Narcolepsy is often linked to the deficiency of a neurotransmitter called hypocretin (orexin), which regulates arousal and wakefulness.

Don't worry if the neurotransmitter names seem tricky. Just remember that Narcolepsy is primarily a biological disorder stemming from the brain's failure to properly control the boundaries between waking and REM sleep.