Biopsych

• Biological Rhythms


  Periodic biological fluctuations in an organism that corresponds to, and is in response to, periodic environmental change
• Endogenous biological rhythms


  Controlled by internal clocks e.g. the suprachiasmatic gyrus
• Exogenous biological rhythms


  Controlled by external, environmental factors e.g. exposure to sunlight
• Exogenous zeitgebers


  External changes in the environment which affect or 'entrain' our biological rhythms
• Circadian Rhythms


  A type of biological rhythm which completes one full cycle every 24 hours e.g. the sleep-wake cycle
• Light is the main example of an exogenous zeitgeber that can trigger desynchronisation of a 'pre-set' sleep-wake cycle
• This demonstrates that prolonged exposure to a strong exogenous zeitgeber such as light, the sleep-wake cycle becomes disrupted and there is a disconnection between psychological time and the clock
• Siffre's sleep-wake cycle did not conform to a cyclical 24 hour-period, but was around 24 hours and 30 minutes, with Siffre himself determining when to sleep and when to eat
• This demonstrates that "there was an internal clock independent of the natural terrestrial day/night cycle"
• Free-running circadian rhythm


  A circadian rhythm that is not affected by exogenous zeitgebers
• Aschoff and Wever (1967) experiment

  1. 55 participants deprived of natural light whilst spending 4 weeks in an underground bunker

  2. All subjects showed free-running circadian rhythms, with the average periods of wakefulness and sleep ranging from 23.9 to 50.0 hours

  3. 36 subjects remained internally synchronized during the whole experiment
• These findings demonstrate that although the free-running circadian rhythm is more than 24 hours long, as a society we have specific exogenous zeitgebers which entrain the rhythm to conform to a 24 hour cycle
• Free-running circadian rhythm


  Circadian rhythm that is not affected by exogenous zeitgebers
• Free-running circadian rhythm


  • Aschoff and Wever (1967) study where 55 participants were deprived of natural light whilst spending 4 weeks in an underground bunker
• The free-running circadian rhythm is more than 24 hours long, but society has specific exogenous zeitgebers which entrain the rhythm to conform to a 24 hour cycle
• Delaying the starting time of Monkseaton High School to 10 AM instead of 8 AM


  GCSE results went up from 34% of pupils scoring 5 A*-C grades including English and Maths, to 53%. For disadvantaged students, the rates of scoring 5 A*-C grades increased from 12% to 42%
• Artificial lighting can create shifts in circadian rhythms by up to 6 hours
• Boivin et al. - shift work

  found circadian troughs are at 6 AM = lowered concentration lead to more accidents

  
  

  Further research found 3 X more likely to develop heart disease
• Individual differences in the duration and stages of circadian rhythms has been shown
• Infradian rhythm


  Biological rhythm with a frequency of one complete cycle occurring less than once every 24 hours
• Infradian rhythms


  • Menstrual cycle
  • Seasonal affective disorder (SAD)
• McClintock et al (1998) demonstrated menstrual cycle synchronisation amongst 29 women who all had irregular periods
• Seasonal affective disorder is an infradian disorder caused by disruption to the sleep-wake cycle, and commonly occurs in the winter
• Ultradian rhythm


  Biological rhythm with a frequency of one complete cycle occurring more than once every 24 hours
• Ultradian rhythms


  • Stages of sleep
• Dement and Kleitman (1957) studied 33 adults and found discrete periods of rapid eye movement potentials were recorded without exception during each of 126 nights of undisturbed sleep
• Trevathan et al (1993) found no evidence of menstrual synchronisation in the all-female participants used
• Gloth et al (1999) found that treating sufferers of SAD with Vitamin D supplements resulted in a 74% improvement in their depression measures, while phototherapy showed no significant change
• Luo et al (2003) found that mammals encode social and reproductive information by integrating vomeronasal sensory activity specific to sex and genetic makeup
• Endogenous pacemakers


  Internal bodily regulators of biological rhythms, affecting or 'entraining' such biological rhythms to conform to certain cyclical periods
• Suprachiasmatic nucleus (SCN)


  • Receives information about day light and day length from the eyes, and triggers different rates of release of melatonin from the pineal gland

  
• DeCoursey et al (2000) found that the vast majority of chipmunks with surgically lesioned SCNs were killed within the first 80 days after being returned to their habitat
• Ralph et al found that the restored rhythms always exhibited the period of the donor genotype, regardless of the direction of the transplant or genotype of the host
• Exogenous zeitgebers


  External environmental changes, affecting or 'entraining' biological rhythms to conform to certain cyclical time periods
• Exogenous zeitgebers


  • Set meal times and bed times
  • Light
• Damiola et al demonstrated that the circadian rhythm of mice liver cells could be influenced to experience a 12 hour discrepancy, leaving the SCN unaffected
• Miles et al (1977) reported the case of a man with a sleep-wake cycle of 24.9 hours, which could not be changed through the use of either stimulants or sedatives