Sleep definitions

Sleep

A state of partial or total loss of consciousness in which mental and physical activity are reduced.

According to adaptation theories of sleep, there are two main reasons why humans became motivated to sleep during the night: evolutionary and restorative reasons.

Evolutionary Purpose

Sleep serves as a means to increase an animal’s or human’s chance of survival in its environment.

Sleeping at night conserves energy, sleep depends on animal’s vulnerability to predators, and the need to find food.

Restorative Purpose

Sleep allows us to recharge our bodies, growth to occur, recovery from work in the day.

Recuperation theories claim homeostasis is disrupted when humans are awake, so sleep acts to restore it.

Sleep restores energy levels that decline in wakefulness such as:

• repairs and replenishes the body

• enhances mood

• increases alertness

• Activates growth hormones

• increases immunity to disease

Sleep-wake cycle

The reoccurring 24-hr pattern of wakefulness and sleep. Typically, this consists of 16 hours daytime wakefulness and 8 hours of nighttime sleep. This is measured by recording times of regular events such as meals, bedtime.

Regulation of Sleep-wake cycle

Regulated by circadian rhythm, body temperature, metabolic rate, and release of hormones including melatonin and cortisol.

Circadian rhythm

A natural bodily cycle that responds to external cues. They can be reset by exposure to external stimuli such as heat and light. For example, Jet lag comes before circadian clocks sync up with local time.

Master Circadian Clock (MCC)

Regulates most of the circadian rhythm. It functions to coordinare biological processes so they occur at a time that maximises individuals’ fitness.

Location of MCC

Located in the hypothalamus in a cluster of neurons called the suprachiasmatic nucleus (SCN). These neurons receive input about the duration and intensity of light detected by the eyes, and coordinate timing of body’s circadian rhythms.

Types of Circadian rhythm Cycles

Body temperature cycle, hormone secretion cycle

Body temperature cycle

Naturally drops at night and rises during the day.

Hormone secretion cycle: Melatonin

Melatonin is a hormone released by the pineal gland which increases in the evening to promote sleepiness, and decreases in the morning in response to light to support wakefulness.

Hormone secretion cycle: Cortisol

Cortisol is a hormone released by the adrenal glands, peaking in the morning to help us wake, and decreases at night to allow rest. Cortisol awakening response promotes alertness and boosts blood sugar.

Cycles relationship

While body temperature, melatonin, and cortisol secretion are separate circadian rhythms following their own cycles, they are tightly linked and help regulate the sleep-wake cycle.

Sleep cycle in action - types of sleep

NREM: repairs and restores the body

REM: repairs and restores the brain *rapid eye movement, dreaming

Typical adult sleep cycle:

• 4 to 6 cycles per night

• Each cycle duration is 90-110 minutes

• Each cycle will vary slightly in length, presented in a hypnogram

Typical pattern of cycles

NREM 1 - NREM 2 - NREM 3 - NREM 2 - NREM 1 OR REM

Sleep latency

The time it takes to fall asleep, ideal is from 9-19 minutes

NREM 1

Sleep state: Lightest, transitional period between wakefulness and sleep

Heart rate: Begins to slow down, may show minor fluctuations

Eye movement: Slow rolling and stops once asleep

Muscle Tension: Starts to relax, as muscle tension decreases hypnic jerks may occur

Brainwave patterns: Alpha waves that change to theta waves

NREM 2

Sleep state: Light sleep

Heart rate: Becomes more regular and slower

Eye movement: Eve movements stop

Muscle Tension: Continues to decline, occasional minor muscle twitches

Brainwave patterns: Theta waves along with sleep spindles and K-Complexes

Sleep Spindles

Bursts of low amplitude, high frequency brain activity lasting about one second.

K-complexes

Single, large bursts of high amplitude, low frequency brain waves

NREM 2’s role

With sleep spindles and K-complexes, they play an important role in declarative memory consolidation. Newly learnt information and experiences are transferred from short-term memory to long-term memory, strengthening neural connections and integrating new memories with existing knowledge.

NREM 3

Sleep state: Deep Sleep

Heart rate: Steady and at its lowest

Eye movement: No eye movement

Muscle Tension: At its lowest

Brainwave patterns: Predominantly delta waves

NREM 3’s Role

NREM 3 is essential for physical restoration, tissue repair and immune system functioning.

Plays a major role in memory consolidation though is less significant than Stage 2.

REM sleep

Sleep state: Vivid and memorable dreams

Heart rate: Irregular, may increase, sometimes reaching similar levels to wakefulness

Eye movement: Rapid and Jerky

Muscle Tension: Virtually absent, muscles are temporarily paralysed except for those involved in breathing and eye movement.

Brainwave patterns: Beta-like waves including sawtooth waves

REM’s role

REM is often called paradoxical sleep, as the brain is highly alert whilst the body is immobile. It involves minimal physical restoration because muscle atonia prevents movement.

REM plays a role in procedural memory consolidation, as well as helping to regulate and process emotions, and supports creative problem solving, new ideas and connections during dreaming.

Sawtooth waves

Fast, randomly occurring waves, slightly larger than alpha waves. They reflect dreaming and heightened neural activity.

Brain wave patterns

Measured with an electroencephalogram (EEG) that measures electrical brain activity in real time.

Beta Waves

Low amplitude, high frequency

Alpha waves

Low to medium amplitude, low to medium frequency

Theta waves

Medium to high amplitude, medium to low frequency.

Delta waves

High amplitude, low frequency

Sleep deprivation

The condition of not getting enough sufficient sleep.

Causes of sleep deprivation

Shift work, Drugs, Sleep Environment, Stressors

Shift work

Impacts the hours of sleep due to sleeping during the day and being awake at night. Hormones that are secreted will be impacted, reducing both the quality and duration of sleep (cortisol and melatonin are disrupted, directed by light exposure)

Drugs

Drugs can impact the progression of sleep stages, reducing both NREM and REM sleep.

Caffeine is a stimulant drug that delays the onset of sleep.

Alcohol is a depressant drug that causes nighttime awakenings, and reduced REM sleep, can increase snoring and sleep apnea, reducing sleep quality. The body has rested but the brain has not, deep sleep is unlikely as snoring can cause wakings.

Sleep environment

Light can cause interruptions to melatonin production. This prolongs falling asleep and reduces duration.

Environmental noise can cause awakenings and reduce sleep quality.

Temperature and air quality can also play a role in the quality of sleep.

*Sleep duration being optimal does not equal sleep quality being optimal

Stressors (sleep deprivation)

If an individual is dealing with a stressor (eg exams) they are likely to experience difficulty falling asleep and anxiety.

Anxiety can then cause difficulty falling asleep; this becomes a cycle.

Increased sleep latency (over 15 minutes)

Acute Sleep Deprivation

Occurs because of a short-term lack of sleep over a 24-hour period, or up to a few consecutive nights. However, there is no exact number of hours constituting for acute sleep deprivation, but generally less than 5 hours within a 24-hour period.

Acute Sleep Deprivation causes

Commonly due to staying up late, pulling an all-nighter, jet lag, stress

Acute vs Chronic

Acute sleep deprivation is short-term and can typically be reversed with adequate sleep, whilst chronic is long-term and overall health outcomes are more difficult to reverse.

Chronic sleep deprivation

Characterised by inadequate sleep for more than a few weeks at a time, sometimes lasting for years.

Chronic sleep deprivation causes

Sleep disorders such as insomnia, or continual disturbances to sleep, or expensive periods of insufficient sleep due to long work hours or lifestyle choices.

Acute Sleep deprivation psychological effects

Attention overall is reduced and decreased lapses of attention, focus is temporarily lost. Occurs because cognitive processing slows and brain struggles to take in/retain new information, making it harder to concentrate and learn effectively.

Mood can be significantly altered, reducing positive emotions and increasing negative emotional responses to stressors. This often results in irritability, frustration, and feelings of anger.

Acute sleep deprivation physiological effects

Reflex speed (time it takes for signals to travel between neurons). Reaction time incorporates reflex speed and cognitive processing. Sleep deprivation slows both processes = longer reaction times and delayed responses to stimuli. Both sleep loss and alcohol impair the brain’s ability to process information, slowing down reflexes.

Vision, much like the brain and body, the eyes repair themselves during sleep. Without enough sleep, eyes become itchy, dry, or bloodshot, and tear production may decrease, increasing risk of eye infections. Can also cause blurry vision, involuntary eye twitches (spasms), and increases sensitivity to light.

Chronic sleep deprivation psychological effects

Anxiety: risk factor for anxiety disorders because sleep plays an essential role in regulating emotions. When sleep is consistently disrupted, this regulation is impaired, leading to heightened feelings of anxiety. REM deprivation specifically, overstimulates limbic brain structures (involved in regulating emotion, behaviour, motivation, memory). Heightened brain activity contributes to increased irritability and reactivity. Anxiety disorder individuals can have symptoms worsened by insufficient sleep.

Chronic sleep deprivation physiological effects

Heart disease: stress hormones (cortisol) are elevated, as well as cholesterol and blood pressure levels being increased. Overtime, these changes place pressure on the cardiovascular system and increase risk of developing heart disease.

Obesity: Sleep deprivation disrupts the balance of hormones regulating appetite including Ghrelin (stimulating hunger) and Leptin (signally fullness). Hormonal imbalance causes individuals to consume more high energy foods and increase overall food intake, contributing to weight gain and obesity.

Chronic sleep deprivation effect: Insomnia

Insomnia differs to other effects, as it has both physiological and psychological components, which can result in sleep deprivation. Insomnia is a sleep disorder characterised by difficulties falling asleep (onset) or difficulties staying asleep (maintenance). It is common to wake up not feeling well rested.

Sleep hygiene

The behaviour and sleep environment that contribute to healthy sleep.

Patterns relating to sleep hygiene can act as cues in our environment.

Zeitgebers

Cues in the environment that provide signals to do things at certain times.

Management of electronic devices

Electronic devices emit blue light which inhibits melatonin production, disrupting the circadian rhythm, making it difficult to fall asleep.

It is recommended to use no electronic devices one hour before bedtime.

This is because blue light stimulates the SCN, and light detection changes/resets MCC, decreasing sleep duration and quality, and increasing sleep latency.

Brain stimulation results from electronic device use.

Consistent Pattern of Sleep

Consistent sleep routine/pattern regulates our circadian rhythm, in terms of following the guide for sleep hours as directed by our age/development. Consistency increases duration of sleep, and decreases sleep deprivation (acute).

Creation of a healthy sleep environment

Circadian rhythms can be disrupted by an uncomfortable sleeping environment. The recommended sleep environment is dark, quiet, cool, and free from distractions.

In creating this, bed is for sleep and intimacy only (to avoid wakeful associations and stimulate brain activity during bedtime), air flow and ventilation are important, and temperature should be between 16-20 degrees (low temperature activates NREM 3).

Study: Restricting Bedtime mobile phone use

He et al, 2020

Aim

To determine how limiting the use of mobile phones before bedtime affects mood, working memory, pre-sleep arousal, sleep quality, and sleep habits.

Method

Participants: 38 University Students conveniently sampled from the Second Military Medical University (China), all with the habit of using their mobile phone before bed, and poor sleep quality.

Materials: PANSAS, n-Back task, PSAS, PSQI, Online sleep diary

Design:

IV: The use of a mobile phone during bedtime vs no mobile phone 30 minutes before bedtime

DV: Mood, working memory, pre-sleep arousal, sleep quality, sleep habits

Procedure

1. Researchers obtained approval from ethics committee. 38 University students conveniently sampled from Second Military Medical University (China) all with the habit of using their mobile phone before bed, and poor sleep quality, via a social media ad. Informed consent obtained.

2. All participants completed tests to measure DVs, Self report diary being filled out a week in advance.

3. Participants are randomly allocated to Experimental or Control group. 19 in each.

4. For the next four weeks, participants in the experimental group obstained from using their mobile phones 30 minutes before bedtime. Control group continued to use their phones as normal.

5. After the four week mark, all participants complete the same tests again. Results were compared.

Key Findings

Participants who avoided mobile phone use 30 minutes before bed fell asleep faster (reduced sleep latency), slept for longer (sleep duration), experienced better sleep quality, reported lower pre-sleep arousal, greater positive affect, less negative affect and showed improved working memory.

Results of sleep quality measured with PSQI at pretest, and after four weeks is shown with lower PSQI scores, indicating better sleep quality.

Contribution to Psychology

Relatively recent study using reliable measures (PSQI used since 1989), increases potential for study replications.

Replications = assess reliability of the study

Criticisms and Limitations

Small sample size = limited generalisability

Four weeks is too short to examine long term effects

Apart from n-back, all measures are self report, producing subjective data. Ideally, this should be paired with physiological measures to provide less biased, objective data.

Positive and Negative Affect Schedule (PANSAS)

• Self-report measure (Subjective, quantitative) with 20 statements and a 5-point Likert scale for each

• Positive and negative emotions over the past week are assessed

n-Back task

• Working memory is tested

• Computer program presents multiple series of numbers and required to respond when a specific number was presented/when two identical numbers appeared right after the other/when a number was identical to the number that appeared two numbers prior

• Performance measures through observable outcomes

  • Reaction time and accuracy (Objective, quantitative)

Pre-sleep Arousal Scale (PSAS)

• Self-report measure

• 5 Point Likert scale for each 16 statements (pertain to cognitive and somatic arousal experienced when trying to fall asleep)

  • Cognitive: Thoughts

  • Somatic: Physiological symptoms

Pittsburgh Sleep Quality Index (PSQI)

• Self-report measure

• 19 items that assess sleep quality (eg “What time do you usually go to bed at night”) over the past month

• High score of 21 indicates poor quality

• Score above 5 indicates sleep disturbances

Online Sleep Diary

• Self-report measure

• Daily record includes:

  • Bedtime

  • Sleep latency

  • Wake time

  • Sleep duration

  • Time arisen from bed

  • Screen time (between 9pm and sleep)

  • Screen time (during the day)