Topic 2- biological rhythms

• biological rhythms 


  • these are the rhythms that govern much of our physiological functioning
  • our bodies use cues from its own internal processes and from the environment
  • in this topic we are looking at biological rhythms and the impact they can have in our behaviour when disrupted
  • circadian- cycle of sleep
  • ultradian- blood circulation
  • infradian- menstrual cycle
• Siffre

  • he lived in a cave 400 feet underground for 2 months
  • he lost track of time but his had kept its own time
  • Siffre phoned the surface every time he ate, woke up and when he was going to sleep
  • these times coincided with when most people eat, sleep and wake up
  • although the cycle was closer to 24 hours and 30 minutes rather than 24 hours, this was used as evidence to suggest that our bodies have internal clocks
• Preckel et al


  • 272 German students took the Lark-Owl chronotype indicator, parents also filled in the questionnaire about their child
  • it was found that being an owl was a significant negative predicator of overall grade point average. this was still significant after many factors were controlled for
• Melatonin pills


  • the supracjiasmatic nucleus detects changes in light levels from the environment, when light levels are low, it instructs the pineal gland to release melatonin which induces sleep
  • taking melatonin could help people when they need to get to sleep earlier than their body would naturally want to
  • Herxheimer and Petrie found that 9/10 studies showed that melatonin was an effective treatment for jet lag
• light therapy


  • phototherapy involves sitting near a light box, which emits artificial light.
  • if used at the start of a night shift, it would reduce the production of melatonin and trick the body into thinking it it still day time
  • costa et al- found light therapy improved physical fitness, sleep patterns feelings of tiredness and improved performance of nurses working a night shift compared to when working under normal lights
• Czeisler- aims

  • to investigate the effects of taking into account circadian rhythms when designing work schedules- specifically the direction in which shifts are rotated and then intervals between these shifts
• Czeisler- sample


  • workers at a potash factory
  • for 20 years they had been using a 7 day work schedule, you would do an 8 hour shift and then after a week move to the preceding shift: midnight to 8am, 4pm to midnight, 8am to 4pm (a phase advancing schedule)
  • 153 male employees, 85 on rotating shifts, 68 as a control group
• Czeisler- measures

  • self-report measures found that those on the rotating shifts had more issues with insomnia
  • those on rotating shifts reported falling asleep at work more frequently and they also complained more about the work schedule
• Czeisler- intervention


  • he educated all employees on the sleep cycle and moved everyone to a phase delay schedule
  • half of the 85 shift workers still changed schedule every 7 days, the other half changed every 21 days
• Czeisler- results

  • significantly more workers preferred the new phase delay work schedule
  • less complaints about changing work schedules with the 21 dt schedule
  • staff turnover for 21 dat schedule was comparable to control group
• Czeisler- conclusion


  • for schedules that use phase delay and increase the gap between changing shifts leads to happier employees