Sleep States


Sleep States

The Nature of Sleep

  • Sleep is a different state of consciousness where responsiveness to the external environment is diminished.
  • Sleep occurs daily as a circadian rhythm, and is composed of an ultradian cycle of seperate stages.
  • Psychologists are able to investigate the brain activity which occurs during sleep by the use of electroencephalograph. This helps them conclude that sleep is composed of identifiably different sequential stages.

The Physiology of Sleep:

  • The brainstem has a role in key functions, including the controls of sleep behaviour, which has severaly hormones involved too.
  • The superchiasmatic nucleus reacts to different levels of light received by the eyes, stimulating the production of melatonin from the pineal gland; this then stimulates the release of serotonin in the reticular activating system.
  • The increase in serotonin levels causes RAS activity to lessen, bringing on the onset of sleep.
  • The release of noradrenaline causes the onset of REM sleep.
  • Acetylcholine is involved in the brain activation during wakefulness and REM sleep, sometimes referred to as wakeful sleep.
  • As sleep has five stages, it is likeltly that each stage has a different function.
  • REM sleep is identifiable in warm-blooded but not cold-blooded creatures, suggesting that it might be that REM sleep serves the function, by increasing brain metabolism, of keeping brain temperature at a safe level.

Issues, Debates and Approaches:

  • Much research into the nature of sleep can be seen as reductionist, such as dividing sleep into seperate stages on the basis of EEG readings.
  • Descriptions of the nature of sleep can be argued to be deterministic, seeing sleep as a behaviour over which humans have little, if any, control over.

Lifespan changes

  • Lifespan changes are a crucial determinant of the amount of sleep people need.
  • Sleep needs to vary by age, both qualitively, in terms of the different stages of sleep, and quantitatively, in terms of how much sleep is needed.

Prenatal Sleep:

  • It is difficult to tell much about foetal sleep patterns.
  • Prenantal sleep cannot be compared to premature babies EEGs, because they are surrounded by different exogenous zeitgabers, which will make the comparison not valid.
  • Okai (1992) - studied REM and NREM sleep in unborn babies of 30 pregnant women and found that NREM phase could be identified by 32 weeks. This correlates with development of neural structures in the brain known to be responsible for sleep stages.

Infant Sleep:

  • Infants display active sleep, an immature form of REM, which gradually decreases, while the amount of quite sleep, an immature of slow-wave sleep, increases.
  • Newborns spend 17 hours a day sleeping, but there is big individual differences.
  • An infants REM sleep is often quite restless, with its arms and legs and the muscles of the face moving almost constantly; they spend 50% of their sleep in REM sleep.
  • Newborn babies often enter REM sleep immediately and its not until 3 months old that the sequence of REM/NREM sleep is estabilished.
  • Over the first few months, the proportion of REM sleep decreases rapidly, a regular pattern


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