exogenous zeitgebers

• exogenous zeitgeber definition

  • External environmental factors that reset biological clocks
  • Resetting biological clocks is a process known as entrainment
  • Without external cues, the free-running biological clocks continues to ‘tick’ in a cyclical pattern
  • Zeigebers rest the sleep/wake cycle(interaction of internal and external factors)
• light = key EZ that influences the sleep/wake cycle

  • light can reset the body’s main endogenous pacemaker (SCN) and also has an indirect influence on key processes in the body controlling hormone secretion, blood circulation etc
  • Campbell and Murphy:
  • Woke 15 participants at various times and shone a light on the backs of their knees
  • producing a deviation in the sleep/wake cycle of up to 3 hours
  • Light does not necessarily rely on the eyes to influence the SCN
• social cues = have an important influence on the sleep/wake cycle

  • The sleep/wake cycle is fairly random in human newborns, but most babies are entrained by about 16 weeks
  • Schedules imposed by parents are a key influence (including adult-determined mealtimes and bedtimes)
  • Research on jet lag:
  • Shows adapting to local tines for eating and sleeping (not responding to one’s own feelings of hunger and fatigue) entrains circadian rhythms and tackles jet lag
• limitation = EZs differ in different environments

  • EZs do not have the same effect on people who live in places where there is very little darkness in summer and very little light in winter
  • Eg = those living in the Arctic Circle have similar sleep patterns all-year round, despite sending around 6 months in almost total darkness
  • Suggests the sleep/wake cycle is primarily controlled by endogenous pacemaker makers that can override environmental changes in light
• limitation = case study evidence undermines effects of exogenous cues

  • Miles et al = reported the case of a man (blind from birth) with an abnormal circadian rhythm of 24.9 hours
  • despite exposure to social cues (such as meal times) his sleep/wake cycle could not be adjusted
  • Suggests that social cues alone are not effective in resetting the biological rhythm and the natural body clock is stronger
• extra evaluation = age-related insomnia

  • Natural changes in circadian rhythms mean older people fall asleep early and have poorer quality sleep
  • BUT = Hood et al = found that management of insomnia improved if elderly people were more active and had more exposure to natural light during the day
  • suggests that exogenous changes in lifestyle may be just as likely to cause age-related insomnia as internal, biological changes