Biological Rhythms Flashcards
Define circadian rhythms
Distinct patterns of changes in body activity that conform to cylical time periods; can be influenced by internal body clocks or external changes
Describe Siffre case study on Circadian rhythms
Michael Siffre spent extended periods underground to see effect on biological rhythms
- resurfaced in Sept after 2 months; believed it was August
- repeated this for 6 months
- found biological rhythms settled beyond usual 24 hours (~25 hrs) but continued to wake up and fall asleep on a normal schedule
Describe Aschoff and Rutger study into circadian rhythms
-convinced group of ppts to spend 4 weeks in a WW2 bunker
-almost all ppts displayed a circadian rhythm of 24-25hrs
What are findings of studies into circadian rhythms?
Both studies suggest our natural sleep/wake cycle is slightly longer than 24hrs but has been entrained by exogenous zeitgebers (e.g. daylight hours, typical mealtimes,etc.)
- our internal body clock is free running and maintains a cycle of 24/25h despite external cues
Give positives of circadian rhythms
+ Practical application –> research shows night shift workers suffer a concentration lapse at 6am, increasing chance of accidents + shift workers are x3 likely to suffer heart disease due to adjusting to sleep/wake cycle
- has economic implications, in maintaining worker productivity and preventing workplace accidents
+ Application in pharmacokinetics –> can help determine best time to administer drug treatments e.g. reducing risk of heart attack by taking drugs at night
- optimum times for administration + dosage of drugs to increase efficacy
Support from cave study –> suggests bodys internal clock is set 24-25hrs in absence of external cues, intolerant of any major alterations to sleep/wake cycle through processes like shift work or jet lag
Give negatives for circadian rhythms
Issues with case study evidence
- Siffre was only one individual and other studies were conducted on small samples
- impossible to generalise results to entire population; may be due to individual difference (e.g. Sidfre noticed differences when he went into the cave at 60yo)
Poor control in studies
- in cave studies exposure to artificial lights (torches/phones) was not controlled
- assumed only natural light has an effect on circadian rhythms but it was found artificial light can also adjust them
- means research lacks validity and so sleep/wake cycle may vary considerably more
Define infradian rhythm
Biological rhythms lasting more than 24 hours
Define ultradian rhythm
Biological rhythms which last under 24 hours (ultradian = under)
Give examples of infradian rhythms
Menstrual cycle, seasonal affective disorder
Describe the menstrual cycle
28 day cycle with a 6 day period of fertility; with biological changes such as ovulation, thickening of womb lining and shedding of womb lining (menstruation)
Which hormones control the menstrual cycle and what changes are caused?
Oestrogen and progesterone
~ increase in oestrogen causes ovulation
~ progesterone helps grow womb lining
Describe seasonal affective disorder
Depressive disorder with seasonal pattern onset
~ particular type of infradian rhythm = circannual (yearly)
What hormone leads to SAD and why?
During winter melatonin is secreted for longer, suppressing serotonin production
Describe sleep cycle
Alternates between REM (rapid eye movement) and NREM (non-rapid eye movement) sleep + consists of 5 stages
What are the stages in the sleep cycle?
Light —> Deep —> REM sleep; here brain waves speed up and dreaming occurs
- one cycle lasts 90 minutes
- goes through 4 stages of NREM then REM + repeats
What research supports ultradian rhythms?
Dement and Kleitman
~ monitored sleep patterns of 9 adult ppts + recorded brainwave activity with an EEG
~ found REM activity = highly correlated with experience of dreaming; brain activity varied according to how vivid dreams were
~ recall of dreams better during REM
~ shows REM is a distinct stage
Give strengths of research supporting ultradian rhythms
Objective measurement —> use of EEGs has high internal validity
Control of extraneous variables —> controlled for effects of caffeine + alcohol, gives us more certainty differences in recall or brainwaves are not affected by other factors
Give limitations of research supporting ultradian rhythms
Small sample —> only 9 ppts, may be unrepresentative so cannot be generalised to whole pop., may tell us little about sleep patterns
Beta bias —> 7 males vs 2 females; study may actually tell us little about sleeping patterns of women
Low ecological validity —> artificial lab setting may have affected sleep patterns, producing abnormal results
Self-report —> ppts reported their own dreams and may show SDB or demand characteristics; cannot be sure if recall is accurate, lowering IV
Describe study into menstruation as an infradian rhythm
McClintock
- studied 29 women with an irregular period
- gathered pheromone samples of 9 of the women; applied these to the other ppts over the 28 day cycle
- found 68% of women experienced changes which brought their cycle closer to their ‘odor donour’s cycle
- shows menstrual cycle is influenced by exogenous factors (other women’s pheromones)
Evaluate research into menstruation as an infradian rhythm
Small sample
Uncontrolled variables —> stress, diet, exercise; may have explained changes in menstrual cycle rather than donor, no causation is established
Describe practical application of SAD
Phototherapy —> using light box in mornings and evenings; limits melatonin production, therefore increasing serotonin
- Eastman et al found it relieved symptoms in 60% of individuals
Give limitation of practical application of SAD
Eastman et al also found 30% of ppts using a placebo reported relieved symptoms
- may suggest condition is not actually linked to melatonin
