!!! Biological Rhythms Flashcards
Czeisler et al- key research
Background: Czeisler et al investigated rotating shifts at a potash production plant in Utah USA. The facility operated a rotating shift system: midnight to 8am (night shift), 8am-4pm (day shift) and 4pm-midnight (swing shift). Employees would change shifts every 7 days in a phase- advance direction.
Sample: 153 male employees with comparable jobs:
- 85 employees 19-68 working on rotating shifts.
- They were compared against a control group of 68 employees 19-56 who’s shifts didn’t rotate and worked either day or swing shifts.
Procedure: self reports conducted to find employees experience of the shift system. They were then given a presentation on the circadian sleep-wake cycle and suggestions on how to adjust their sleep time to fit their work schedule. The 85 ratating shift workers were moved to phase delay:
-33 continued to rotate shifts every 7 days, 52 rotated shifts every 21 days.
To assess the impact of the intervention, he:
-after 3 months, gave workers questionnaires to fill in about their preference.
-after 9 months, personal turnover and plant productivity were analysed.
Results:
- initial self report found 29% of employees on rotation shifts had fallen asleep at work in the previous 3 months. 81% said it took 2-4 days for their sleep schedule to adjust after each phase advance.
- Post-intervention questionnaire showed they preferred the phase delay shift rotation and those on the 21 day shifts were happier (and more productive) than those on the 7 day.
- 21 day shift had no more staff turnover than comparable group of non-rotating shift workers.
Conclusion: shifts should rotate in a phase delay direction and rotate the schedules less often.
Siffre- living underground
French scientist Michel Siffre lived 400 feet below the surface in a cave in the French- Italian Alps for 2 months in 1962. The cave was completely dark apart from a lightbulb and he had no contact with the surface apart from when he informed them when he slept and woke up. Temp in the cave was below freezing and humidity was 98%.
As Siffre was able to sleep for as long as he wanted to, it was found that his body followed the same sleep-wake cycle every 24 hours 30 minutes instead of 24 hours. This shows humans have an internal body clock independent of the natural terrestrial day/night cycle.
Preckel et al- German high schools
A sample of 272 German high school students in 5 schools in the 9th and 10th grade were given a chronotype questionnaire (lark/owl) and then a standardised cognitive test. Parents of 132 of the children also filled in a questionnaire rating their child’s chronotype.
Results showed that students who identified as owls had a lower GPA (in maths -science and language) than larks. Cognitive ability, conscientiousness, need for cognition, achievement, motivation and gender were controlled for.
This suggests that schools having an early start to the school day gives larks an advantage over owls.
Melatonin pills
Normally the suprachiasmatic nucleus detects changes in light levels In the environment and when the light levels get low, it instructs the pineal gland to release melatonin which induces sleep.
Taking melatonin can help people when they need to get to sleep earlier than the body would naturally want to (e.g. when doing shift work).
Herxheimer and Petrie found that in 9/10 studies, melatonin was an effective treatment for jet lag. Take between 10pm and midnight it significantly reduced effects of jet lag when travelling west to east (phase advance).
Light boxes
Phototherapy involves sitting near a light box emitting artificial light. If used at the start of a night shift, it reduces the production of melatonin tricking the body into thinking it’s day time.
Costa et al- found light therapy improves physical fitness and improves sleep patterns while reducing tiredness. It improved the performance of nurses working a night shift compared to working under normal light.
