biological rhythms Flashcards
what happens to cognitive function when deprived of sleep?
declines- the part of your brain that controls language, memory, planning and sense of time is severely affected
what happens after 17 hours of being awake?
leads to a decrease in performance equivalent to a blood alcohol level of 0.05%
what do sleep-deprived individuals have difficulty with?
responding to rapidly changing situations and making rational judgements
what are circadian rhythms?
the sleep-wake cycle that repeats every 24 hours- is this rhythm endogenous- occurring naturally? or exogenous- dependent on external cues like light?
evidence of endogenous (internal) processes?
- demonstrated in plants in 1729 when a french astronomer kept mimosa plants in the dark and found the leaves opened in the morning and closed at night, even without sunlight.
- in 1972, michel siffre lived in a cave below ground for 2 months. it found his body followed a daily sleep cycle of 24.5 hours, rather than 24. suggests humans have a natural internal body clock.
exogenous zeitgebers
light does appear to be crucial in maintaining the 24 hour circadian rhythm.
- campbell and murphy (1998) shone bright lights onto the back of participant’s knees and were able to alter their circadian rhytmns in line with the light exposure.
- possible that blood chemistry was altered and this was detected by the SCN.
- not always the case. social factors reset rhythms, rather than light levels in the arctic circle where it is light for 6 months of the year, but people still sleep for 7 hours avg.
how do circadian rhythms work?
in humans the suprachiasmatic nucleus controls the sleep-wake cycle. it is in the hypothalamus- behind the eyes- and receives information about light levels through the optic nerve. SCN seems to be the location of our main body clock.
- there are things we are aware of (awake and asleep) and some we are not (core body temp changes)
when does body temp peak?
mid-afternoon around 37.1C and troughs in early hours at 36.7C
day to day application
situations where our internal clocks come into conflict with external cues:
- jet lag
- shift work
shift work
in the western world, >20% of workers have permanent or rotating unsocial shift patterns. this results in fatigue, sleep disturbance, digestive problems, lack of concentration, memory loss and mood swings.
what is shift work compounded by?
reverting to normal sleep patterns on days off, and shift patterns altering from one week to the next. this means that people’s biorhythms are in a permanent state of desynchronisation.
what does desynchronisation lead to?
people never adapt to a new rhythm. can result in reduced productivity and risks to their health- heart disease, digestive disorders and regular tiredness. but not everyone has the same tolerance to shifts in their circadian rhythms.
fixed shifts
are rare due to being unsociable, but allow the worker to resynchronise to their new pattern- causes problems during weekends or holiday time where they revert back to a normal sleep-rate pattern.
rotating shifts
working different hours each week/month. cooper (2005) looked at oil rig workers and found those on split shifts never fully synchronised. tests showed higher levels of circulating fatty acids putting them at risk of CHD and hypertension.
what ways can shifts rotate?
clockwise (phase delay) or anticlockwise (phase advance). these can lead to permanent desynchronisation. most research suggests that phase delay is better, but there is disagreement over the speed of rotation
speed of rotation
bambra (2008) said a faster rotation of 3/4 days is better so the body never has time to adjust vs czeisler says that 3 weeks is recommended.
czeisler
looked to alter shifts to improve employees sleeping patterns and circadian rhythms. workers from the same minerals company in utah were compared- some worked shifts, others did not. the shift workers had their patterns altered to see what improved their well-being. clockwise shifts on a 21-day rotation were preferred. follow ups showed this increased staff retention and productivity.
what was czeisler’s study?
a field experiment with a matched group design of participants with comparable jobs.
what did initial self reports show?
rotating shift workers experienced significantly more insomnia than non-rotators:
- 29% reported falling asleep at work
- 90% complained schedule changed too often
- 81% reported it took 2-4 days to adjust sleep schedule
what did czeisler do?
gave all workers a presentation on circadian rhythms that contained suggestions. put them all on clockwise shifts and put 33 on a weekly rotation and 52 on a 21-day rotation.
what were czeisler’s results?
- workers clearly preferred the phase delay shift.
- complaints dropped to 20% on 21-day rotations, and were significantly more satisfied with their schedule than 7-day rotation.
- reported significantly increased scores on a health index
- staff turnover was the same as those on fixed shifts, and productivity increased
what did czeisler conclude?
work schedules that rotate by phase delay with an extended interval between each rotation are most compatible with the properties of the human circadian system. however any new schedule must take into consideration the nature of work and the needs of workers.
strategies to reduce the effect of jet lag or shift work
- schedule changes
- behavioural interventions
- controlled exposure to light and dark
- drugs to promote sleep and wakefulness
schedule changes
- workers have the same shifts with no rotation- although this causes problems for permanent night shift workers on days off- hard to find/keep staff.
- rapidly rotating shifts can improve sleep length and leisure activities, improve blood pressure and reduce use of stimulants.
- giving shifts to those with greater tolerance for abnormal schedules or allow to choose shifts- increase job satisfaction and work-life balance?
- but studies tend to generalise one type of workplace
