ultradian rhythms (biological rhythms)

• Ultradian rhythms:

  • More than once cycle in 24 hours (biological cycles lasting less than 24 hours)
• stages of sleep = ultradian rhythm

  • Sleep pattern occurs in 90-minute periods
  • divided into 5 stages = each characterised by a different level of brainwave activity (monitored using EEG)
• 5 stages of sleep:

  • Stages 1 and 2 = light sleep:
  • Stage 1 = brain waves are high frequency and have a short amplitude (alpha waves)
  • Stage 2 = alpha waves continue but there are occasional random changes in pattern called sleep spindles
  • easy to wake
  • Stages 3 and 4 = deep sleep/ slow wave sleep (SWS):
  • Waves have lower frequency and higher amplitude
  • Hard to be woken
  • Stage 5 = rapid eye movement (REM) sleep:
  • Body paralysed but brain activity resembles that of the awake brain
  • brain produces theta waves and the eyes occasionally moved
  • Dreams mos often experience during REM sleep, but may also occur in deep sleep
• strength = understanding age-related changes in sleep

  • SWS reduces with age = growth hormone is produced during SWS so this becomes deficient in older people
  • van Cauter et al = suggest the reduced sleep may explain impairments in old age
  • SWS sleep can be improved using relaxation and medication
  • Suggests that knowledge of ultradian rhythms has practical value
• limitation = individual differences in sleep stages

  • Tucker et al = found large differences between participants in the duration of stages 3 and 4
  • they suggest that these differences are biologically determined
  • This makes it difficult to describe ‘normal sleep’ in any meaningful way
• extra evaluation = the sleep lab

  • One of the benefits of conducting studies of sleep in lab settings is control of extraneous variables (such as noise or temperature that may affect sleep)
  • BUT = lab studies involve participants being attached to complicated machinery, so their sleep does not represent their ordinary sleep patterns
  • This dilemma means it might be best to conducted some studies in people‘s own homes and compare patterns with records made in lab settings