biological rhythms and endogenous pacemakers and exogenous zeitgebers pace makers Flashcards
what is a biological rhythm?
a change in body processes or behaviour in response to cyclical changes within the environment
what are infradian rhythms?
cycles that last more than 24 hours
what are examples of infradian rhythms?
menstrual cycle
SAD (seasonal depressive disorder)
explain the menstrual cycle
- governed by monthly changes in hormone levels that regulate ovulation
- cycle= time between woman’s period (1st day) to the day before her next period (typical cycles 28 days)
- increase levels of oestrogen causes egg to be released from ovary (ovulation)
- after ovulation progesterone= wombs lining grow thicker and ready for pregnancy if no pregnancy= egg absorbed in body and womb lining leaves body (menustration)
menstrual cycle - what’s the McClintock effect?
- McClintock observed synchronisation of menstrual cycles with uni friends
- asked 135 college girls living in dorms to recall their period start at 3 times during achademic year
- close friend group- periods were on average 6.4 days apart in October (start of academic year) and 4.6 days apart in April (end of achademic year)
- attributed to pheromones (chemical signals that can influence infradian rhythms) to acting as an external zeitgeber
Stern and McClintock study on altering menstrual cycle pheromones.
- 29 women with history of irregular periods
- 9 provided pheromone samples from different cycle stages (wore cotton pad under armpit for 8 hours)
—> day 1 other 20 women smelled the pads from day 1, day 2 smelled day 2 pads etc
—> 68% of the 20 women experienced cycle changes in line with ‘donor’
—> suggests pheromones influences us and act as external zeitgebers
eval of Stern and McCluntock study
- small sample size and self-report methods= lowers validity and demand characteristics ?
- critics say factors like stress and diet also impact cycle (confounding variables) so synchronisation could have just been a coincidence /chance
—> other studies (Travathan et al) found no evidence of menstrual synchrony in all female samples - influence of pheromones= has evolutionary value as for ancestors may have been an advantage for all women to fall pregnant around same time= new borns could be cared for collectively and increase their chance of survival—> BUT now not an adaptive strategy
SAD- what is it?
- depressive disorder and mental disorder in DSM-5
- main symptoms= persistent low mood, lack of interest in life and activity etc
- ‘winter blues’
- symptoms triggered during winter months when number of daylight hours drops
a circannual rhythm as it is subjective to a yearly cycle - can be a circadian rhythm as experience of SAD may be due to disrupted sleep-wake cycle and prolonged periods of darkness in winter
- hormone melatonin implicated in cause of SAD —> during night pineal gland secretes melatonin (hormone that makes us sleepy) until dawn where there’s an increase in light —> in winter lack of light in morning= secretion process continues for longer = knock-on effect on production of serotonin in brain (chemical linked to depressive symptoms)
SAD - eval
- practical applications: phototherapy is used as a treatment (light box that stimulates strong light in morning and evening which resets melatonin levels —> relieved symptoms for 60% of sufferers (Eastman et al) BUT same study found a placebo effect of 30% using a ‘sham negative ion generator’ —> doubt in chemical influence of phototherapy
- bright light therapy is used to treat SAD
—> Anderson et al, its effective non-pharmological treatment - Lambert et al found serotonin production= directly related to sunlight (rising in increased luminosity) and found blood levels of serotonin metabolite= lowest in winter = low serotonin turnover could link to depression and suggests brain serotonin levels may underlie SAD
what are ultradian rhythms?
cycles which occur under 24 hours (less than)
what’s the ultradian rhythm?
sleep stages
sleep stages explain each one
5 sleep stages totalling 90 mins per cycle
- each stage characterised by different EEG activity
stages 1+2
- light sleep, easily woken, brain waves= become slower (alpha waves) as sleep deepens (theta waves)
stages 3+4
- delta waves= slower and have bigger amplitude than previous waves, deep sleep and hard to wake
stages 5
- rapid eye movement (REM), body paralysed but brain activity is the same as when awake, dreaming occurs
ultradian rhythms eval (research support from Dement and Kleitman)
- evidence from Dement and Kleitman who monitored sleep patterns of 9 adults by EEG. They controlled caffeine and alcohol (extraneous variables)
- found REM activity correlated to dreaming. Ppts woken during REM gave vivid descriptions of
- although small sample size used it has been replicated many times and similar findings are found
- but temporal validity lack as now phone etc may influence ppls ultradian rhythm
what are circadian rhythms?
24 hour daily rhythms
e.g. sleep wake cycle and core body temperature
summarise what you mean by sleep wake cycle
we feel drowsy at night and alert during day= demonstrates effect of light and that we have a circadian cycle that corresponds to length of day on earth —> BUT could change if leave clock to its own devices (free running)
circadian rhythms- Siffres cave study
- 1962 a french cave explorer (michael Siffre) spent 2 months living in an isolation in a subterranean cave (no access to clock, sun, calendar)
- he only ate when body told him to
- goal was to discover natural rhythms of human life would be affected by living ‘beyond time’ (free running)
- light came on when he woke and off when he slept
- he settled into a sleep-wake cycle of 25-30 hours (beyond usual 24 hours) —> sleep-wake cycle had become desynchronised
circadian rhythms- Aschoff and Wever bunker study
- placed ppts in a WW11 bunker for 4 weeks with no natural light
- all but one displayed a circadian rhythm of 24-25 hours
—> suggests natural sleep- wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24 hour day (e.g. number of daylight hours, mealtimes etc)
why shouldn’t we overestimate influence of exogenous zeitgebers on our internal body clock? who found evidence for this?
Folkard et al- studied 12 ppl who lived in a dark cave for 3 weeks they sped up they’re clocks to 22 hours a day without ppts knowing, and ppts had to go to bed at 7:45am and wake up at 11:45pm
—> only one ppt could comfortably adjust to the pace of clock= suggests strength of endogenous pacemakers and that exogenous zeitgebers cannot easily override them
what did Siffre and Aschoff and Wevers studies suggest?
suggests we have an internal body clock but in absence of exogenous zeitgebers our sleep-wake cycle is actually slightly longer than 24 hours
who disagreed with the suggestions of Siffres, Aschoff and Wever studies?
- Czeisler et al
- he argues that the use of bright lights are highly artificial and equivalent to powerful drugs —> therefore it must be exogenous zeitgebers (light and social cues) that keep out body in check within 24 hour day
eval point 1 of circadian rhythms
- knowledge = we can understand consequences of disruption of them —> practical applications to shift work
—> night workers experience period of reduced concentration at around 6am (circadian trough) so accidents etc are more likely (Boiwin et al) —> also Knultson found issues with shift work and poor health (3x more linked due to stress of adjusting sleep-wake cycle) —> economic implications on how to best manage worker productivity
eval point 2 circadian rhythms
- practical application - drug treatments
—> Baraldo and research found there’s certain peak times when drugs are most effective as circadian rhythms co-ordinate body processes (heart rate etc)= now guidelines on timing of drug dosing for anticancer etc
eval point 3 circadian rhythms
- use of case studies (Siffre)= not generalisable he was 60 so age may influence results + Siffre used artificial lighting (poor control) and as Czeisler suggested light impacts biological rhythms= lowers ecological validity
eval point 4 circadian rhythms
- Aschoff and Wever used a small sample size
eval point 5 circadian rhythms
- individual differences impact time ppl go to bed —> Duffy et al said some ppl have natural preference to go to bed early and rise early (‘larks’) and others prefer the opposite (‘owls’) —> also age differences in sleep-cycle patterns)
what are endogenous pacemakers?
internal body clocks that regulate biological rhythms e.g. suprachiasmatic nucleus (SCN) on sleep-wake cycle
what is the SCN?
a bundle of nerve cells in hypothalamus in each hemisphere of brain
- influential in maintaining sleep-wake cycle
- nerve cells connected to eye across optic chiasm in way to visual area of cerebral cortex
—> SCN= just above optic chiasm —> SCN receives info about light from the optic chiasm (even when eyes are closed)= enables biological clock to adjust to changing patterns of light whilst asleep)
animal studies and SCN- Patricia Decoursey et al
- Patricia destroyed SCN connections in brains of 30 chipmunks who were returned to natural habitat and observed for 80 days —> their sleep-wake cycle significantly changed by end and lots were killed by predators as awake at vulnerable times
animal studies and SCN- Martin Ralph et al
Martin bred ‘mutant hamsters’ with 20 hour sleep-wake cycle —> when SCN cells from foetal tissue in hamsters was transplanted to normal hamsters brains = their cycles also defaulted to 20 hours
what are the animal studies on SCN evidence of and an eval point on them
- evidence of power of SCN on sleep-wake cycle
- eval- can’t generalise findings of animals to humans and poor ethics (animals were harmed and killed)
what happens at pineal gland?
- it receives info from SCN on day length and light that it receives
- during the night pineal gland then increases production of melatonin (a chemical that induces sleep) and is inhibited during periods of wakefulness
what are exogenous zeitgebers?
- external cues that may affect or entrain our biological rhythms
what does zeitgebers mean?
‘time-giver’
what are the exogenous zeitgebers?
light
social cues
explain the exogenous zeitgeber light
light can reset body’s main endogenous pacemaker, the SCN= plays role in sleep-wake cycle
- light has indirect influence on body processes that control functions like hormone secretion and blood circulation
what did campbell and murphy’s study show on the exogenous zeitgeber light?
- study showed that light may be detected by skin receptor sites on body when when info wasn’t shone on their eyes
- 15 sleeping ppts woken at various times and a light pad was shone on back of their knees—> there was a deviation of up to 3 hours on their usual sleep-wake cycle—> suggests light is powerful and may not need eyes to exert its influence on the brain
ISSUE with study= small sample size and not replicated so lacks reliability etc
explain the exogenous zeitgeber social cues
- infants= seldom on same sleep-wake cycle as family —> initially their sleep-wake cycle is random at around 6 weeks age circadian rhythms start and by 16 weeks most babies are entrained
- schedules on parents= key influence e.g. determine meal and bed times
- adapting to local times for eating and sleeping (rather than responding to your own feelings)= entrain your circadian rhythms and beat jet lag
exogenous zeitgebers and endogenous pacemakers eval part1
- biologically reductionist as other factors e.g. stress etc influence sleep
- ppl can fall asleep in light = may not be as important as research suggests
- Diomala et al showed that changing feeding patterns in mice could alert circadian rhythms in liver by 12 hours inhibit leaving SCN rhythm unaffected —> suggests there’s otehr complex influences on sleep-wake cycle aside the SCN
exogenous zeitgebers and endogenous pacemakers eval part 2
- Shere and Amendt found that blind ppl with some light perception have normal circadian rhythms where as blind ppl with no light perception have irregular rhythms —> evidence of importance of light for internal sleep-wake cycle
- Campbell and Murphy= study can’t be replicated and the way which study was conducted = there may have been some limited light exposure to ppts eyes (extraneous variable) = lowers validity
- only have been a few circumstances where endogenous pacemakers been left free running e.g. Siffres cave study—> total isolation studies= extremely rare and therefore may be judged as lacking validity
