W7: Sleep and Circadian rhythms

definition

  • natural periodic state that involves reduced responses to environmental stimuli and decreased mobility

  • is a bhv observed across cultures and other species - even in unicellular organisms

  • we spend a third of our lives sleeping

2 drives of sleep

  • what makes us go / want to sleep

    • homeostatic (S) process - if we don’t sleep we accumulate sleep dept

    • circadian (C) process - sleep tends to happen at a particular time during the 24h cycle

  • sleep differs from states such as coma (extended period of consciousness), vegetable state

two-process model of sleep

  • homeostatic drive accumulates as we live our day and decreases back when we sleep - ready to start again when we wake up

  • circadian process follows a time of day when we get tires - we need sleep to recharge

the study of sleep - Polysomnography

  • Hans Berger (1929) - discovered the ‘gold standard’ of sleep research

  • initially used cats, now mainly rats (sometimes mice)

  • we get an overall reading of what’s going on in the brain when the person is sleeping

  • use electrodes to read brain activity

polysomnography

  • EEG - recording of activity of populations of neurons in the brain underneath the skull

  • EOG - recordings of activity of the muscles around the eyes to decipher eye movement

  • EMG - recording of the activity of the muscles in the body

  • they can be combined with heart rate an breathing

brain activity during wakefulness

  • different types of neural activity are observed in the EEG recording

    • beta waves - irregular activity of 13-30Hz

      • takes place when the brain is processing information

      • the person is alert and attentive to events in the environment or engaging in cognitive processes

    • alpha waves - activity of 8-12Hz

      • occurs when a person is resting quietly - not particularly aroused or exited and not engaged in strenuous mental activity

brain activity during sleep

  • begins with a state of relaxation , feeling drowsy

STAGE 1

  • 3.5-7.5Hz

  • presence of theta activity - transaction between sleep and wakefulness

STAGE2

  • sleep begins

  • irregular activity and sleep spindles - 12-14Hz

  • although these occur in other stages of sleep and K complexes which are only found during stage 2

STAGE 3

  • high amplitude and low-frequency delta activity (less than 3.5Hz)

  • synchronised regular waves reflecting synchrony and coordination in the activity of neurons in underlying brain areas

  • there is a slowing down of the brain activity as well as other bodily functions, such as heart rate, breathing, temperature, kidney function, etc.

  • referred to as slow-wave sleep (SWS) or deep sleep

REM sleep

  • sleep phase characterised by increased brain activity and asynchrony in brain waves accompanied by muscle atonia

  • Aserinsky and Kleitman (1953) - sleep characterised by rapid eye movement (REM)

  • Michel Juvet (1959) - deep sleep in terms of muscles activity but light sleep in terms of brain activity - Paradoxical sleep

  • facial twitches, erections, vaginal secretions and dreaming occur during this stage

Dreams

  • Dement and Kleitman (1957) - discovered dreams when participants were awakened form REM sleep, they tended to report vivid dreams

  • important in psychoanalysis

    • freud thought of dremans as the ‘royal route to the unconscious’ and an opportunity to realise our secret wishes

    • Jung viewed dreams as a glimpse into the collective unconscious

  • most dreams are related to events that happen in a person’s life

  • Calvin Hall et al. (1982)

    • analysed 10 000 dreams of healthy people and found that more than 64% are associated with sadness, anxiety or anger whereas 18% are happy dreams and only 1% involved sexual content