Psychology: Sleep as a psychological construct

Consciousness

The level of awareness of the internal and external environment.

State of Consciousness

The different states of awareness that we experience. Two categories of state of consciousness are: Normal Waking Consciousness (NWC) and Altered States of Consciousness (ASC)

Normal Waking Consciousness

States of consciousness associated with being awake and aware of stimuli in the external world, of one's sensations, mental experiences and own existence.

3 States of Normal Waking Consciousness

- total awareness
- sustained attention
- normal wakefulness

Altered States of Consciousness

Describes any state of consciousness that is significantly different from normal waking consciousness or any waking state in terms of level of awareness and experience.

7 States of Altered States of Consciousness

- daydreaming
- meditative state
- hypnotised
- asleep
- anaesthetised
- coma
- total lack of awareness

Sleep

A natural and regularly occurring altered state of consciousness that is characterised by partial or total suspension of conscious awareness.

Psychological Construct

A concept, description or explanatory model that describes specific 'psychological' activity or mental processes.

Objective Measures

EEG, EOG, EMG

Electroencephalogram (EEG)

Used to detect, amplify and record electrical activity in the brain through electrodes placed at various points on the scalp.

Frequency

The number of brain waves per second. High frequency brain wave is faster and therefore has more brain waves per unit of time. Low frequency indicates less brain waves per unit of time.

Amplitude

The intensity of brainwaves. High amplitude brain waves have bigger peaks and troughs whereas low amplitude brain waves have smaller peaks and troughs.

Electromyograph (EMG)

Used to detect, amplify and record the electrical activity of the muscles.

Electro-oculargraph (EOG)

Used to detect, amplify and record the electrical activity in eye muscles that control eye movements.

Subjective Measures

sleep diaries, video monitoring, self reports

Sleep Diary

A log used to self-record and self-report sleep and waking time activities over a period of time.

Video Monitoring

To monitor and record externally observable physiological responses throughout a sleep episode, including behaviours when falling asleep and when waking.

Biological Clock

An innate mechanism in living organisms that regulates the cycle of a biological rhythm.

Two Biological Rhythms

Circadian Rhythm and Ultradian Rhythm

Circadian Rhythm

A biological rhythm that involves physiological, psychological or behavioural changes that occur as part of a 24 hour cycle.

Sleep-wake Cycle

A circadian rhythm that regulates cycles of alertness and sleepiness by responding to light changes in the environment.

Ultradian Rhythm

A biological rhythm that involves physiological, psychological or behavioural changes that occur as part of a cycle shorter than 24 hours.

Examples of Ultradian Rhythms

- human sleep
- heartbeat
- respiration
- hunger

Suprachiasmatic Nucleus

Is considered to be the master biological clock that regulates the timing and activity of the sleep-wake cycle.

Regulation of the circadian rhythm sleep-wake cycle by the SCN

1. light is detected by photoreceptors in the retina
2. receptors send neural signals to the SCN
3. SCN receives these neural signals and adjusts the sleep-wake cycle by sending neural signals to the pineal gland
4. the pineal gland receives the neural signals from SCN and secretes more or less melatonin into the bloodstream. The amount of melatonin secreted depends on the amount of light detected by the retina.

Feedback Loop

The melatonin feedback loop enables the SCN to detect the level of melatonin in the blood and modify the output from the pineal gland to maintain an optimal level.

Melatonin

A hormone involved in sleep initiation and regulation of the sleep-wake cycle. It is produced and released into the bloodstream by the pineal gland.

NREM Sleep

Non-rapid eye movement sleep; it encompasses three stages of sleep excluding REM sleep. Approximately 75-80% of our sleep is spent in NREM sleep.

NREM Stage 1

A period of relatively light sleep. It amounts to 4-5% of sleep.
- Physiological Changes: Decrease in heart rate, breathing, body temperature and muscle tension.
- Eye Movements: Slow, rolling eye movements.
- Brain Activity: Lower in frequency from their daylight patterns.
- Hypnic Jerks: Involuntary muscle twitches as a result of the muscles relaxing.
- Arousal Threshold: Low, can be easily awakened

NREM Stage 2

Period of light to moderate sleep, because it gradually becomes deeper. It amounts to 50% of sleep.
- Physiological Changes: Continued slowing of heart rate, breathing, muscle activity and body movements. Body temperature continues to decrease.
- Eye Movements: Begin to stop.
- Brain Activity: Continue to lower in frequency, gradual appearance of slow brain wave activity.
- Sleep Spindles: Brief bursts of electrical activity which occur every 3-6secs.
- Arousal Threshold: Higher than stage 1, but can still be easily woken.

NREM Stage 3

A period of deep sleep. It amounts to 10 to 15% of sleep.
- Physiological Changes: Heart rate and breathing slow to their lowest levels. Muscles are completely relaxed and movement in minimal.
- Eye Movement: None.
- Brain Activity: Become even slower.
- Slow Wave Sleep: The largest and slowest waves become predominant.
- Arousal Threshold: High, difficult to awaken. If woken abruptly, sleep inertia may occur.

REM Sleep

Rapid eye movement; a period of light (brain) or deep (body) sleep. It amounts to 20-25% of sleep.
- Physiological Changes: Heart rate and breathing is faster and irregular. Blood pressure rises, skeletal muscles are limp, so body appears paralysed.
- Eye Movement: Spontaneous rapid bursts of movement of the eyes.
- Brain Activity: Similar brain waves to those seen during alert wakefulness.
- Dreaming: Most dreaming occurs during REM sleep.
- Arousal Threshold: Similar to stage 2 and 3, depends on when during a REM period awakening is attempted.