biological rhythms

biological rhythm

distinct patterns of changes in body activity that conform to cyclical time periods and are influenced by endogenous pacemakers (internal body clocks) and exogenous zeitgebers (external changes in the environment)

ultradian rhythm

rhythms that occur many times during the day

infradian rhythm

rhythms that take longer than a day to complete (if even longer then known as circannual rhythm)

circadian rhythm

biological rhythms that are subject to a 24 hour cycle which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature

circadian rhythm - sleep/wake cycle

daylight is an important exogenous zeitgeber in sleep/wake cycle, suprachiasmatic nucleus (SCN) lies above optic chiasm providing info from eye about light and is an important endogenous pacemaker, exogenous zeitgebers (light) can reset the SCN

Siffre’s research into removal of light stimulus on sleep/wake cycle

deprived of exposure to natural light and sounds but access to food and drink, after spending 2 months in cave in Southern alps, he resurfaced in mid-september 1962 believing that it was mid-august, 1972: spent 6 months in texan cave, free-running biological rhythm settled to 25 hours but still woke up and went to sleep on a regular schedule

Aschoff and Wever’s research into removal of light stimulus on sleep/wake cycle

convinced group of ppts to spend 4 weeks in ww2 bunker deprived of natural light, all but one (29 hours) displayed circadian rhythm between 24-25 hours, natural sleep/wake cycle may be more than 24 hours but it is entrained by exogenous zeitgebers associated with 24 hour day e.g. light

Folkard’s research into removal of light stimulus on sleep/wake cycle

studied group of 12 who agreed to live in dark cave for 3 weeks, going to bed when time said 11:45pm and waking when time said 7:45am, over course of study, researchers gradually sped up clock without ppts knowing so 22 hour days, only 1 ppt was able to comfortably adjust to new regime, existence of strong free-running circadian rhythm cannot be overridden by exogenous zeitgebers

circadian rhythm - core body temperature

varies by around 2 degrees during course of day, lowest at around 4 in morning to 36 degrees, peaks around 6 in evening to 38 degrees, body temperature may have an effect on mental abilities, warmer = better cognition

Folkard’s reserach into core body temperature

children who had stories read to them at 3pm showed superior recall and comprehension to those who heard the same stories at 9am

Gupta’s reserach into core body temperature

found improved performance on IQ tests when participants assessed at 7pm as opposed to 2pm and 9am

strength of research into circadian rhythms - provides understanding of adverse consequences that occur when they are disrupted (desynchronisation) - Bovin et al

night workers engaged in shift work experience a period of reduced concentration around 6 in morning (circadian trough) so mistakes and accidents more likely, real world economic implications of research in terms of how to manage worker productivity

strength of research into circadian rhythms - research used to improve medical treatments

field of chronotherapeutics established - how medical treatment can be administered to correspond to person’s biological rhythms, bonten 2015: aspirin as treatment for heart attacks more useful if taken last thing at night, heart attacks more likely to occur in morning, can increase effectiveness of drug treatment

strength of research into circadian rhythms - real world application in shifting school day

Wolfson and Carskadon 1998: school day should start a little later to fit in with teenage chronotype (sleep pattern) as hormonal changes causes students to be more sleepy early in the day

limitation of research into circadian rhythms - studies regarding effects of shift work use correlation

difficult to establish whether desynchronisation is the cause of these negative effects, solomon 1993: high divorce rates in shift workers may be due to strain of deprived sleep and missing out on important family events, biological factors may not cause adverse consequences of shift work

limitation of research into circadian rhythms - cannot easily generalise due to individual differences

studies based on small samples, czeisler 1999: found individual differences in sleep/ wake cycles varying from 13 to 65 hours, difficult to use data to discuss anything more than averages which could be meaningless

limitation of research into circadian rhythms - shifting school day can be disruptive

parents and teachers disturbed pattern, limits number of extracurricular activities, would not reduce sleep deprivation as teenagers would still stay up later

menstrual cycle - infradian rhythm

oestrogen causes ovulation and progesterone thickens uterus lining, if egg is not fertilised the lining is shed and leaves as menstrual blood, although it is endogenous system it is influenced by exogenous factors such as the cycles of other women

sample of stern and mc clintock’s research into menstrual cycles

studied 29 women with history of irregular periods

method of stern and mc clintock’s research into menstrual cycles

pheromone samples gathered from 9 of the women by placing cotton pad in armpit for 8 hours then treating pad with alcohol and freezing, pad rubbed on upper lip of other participants pads from start of menstrual cycle applied on day 1, pads from second day applied on day 2 etc.

findings of stern and mc clintock’s research into menstrual cycles

68% of women experienced changes in their menstrual cycle which brought them closer to the cycle of the odour donor

seasonal affctive disorder - infradian rhythm

persistent low mood, triggered during winter months when hours of daylight become shorter, type of circannual rhythm as subject to yearly cycle but can also be classed as circadian rhythm, melatonin is implicated in cause of SAD as during night, pineal gland secretes melatonin until light detected, during winter lack of light means melatonin secreted for longer which effects release of serotonin

strengths of resarch into infradian rhythms - can be explained by natural selection

advantageous for women to menstruate together and become pregnant at same time in past, allows babies who have lost their mothers to have access to breastmilk increasing survival chances

strengths of resarch into infradian rhythms - real world application in treatment for SAD

sanassi 2014: light therapy helps reduce the effects of SAD in about 80% of people, light therapy better than antidepressants because it is regarded as safer

methodological limitations of research into infradian rhythms

many factors affect menstrual cycle e.g. stress, changes in diet, exercise which act as confounding variables so findings are due to chance, trevathan 1993: failed to replicate findings, less reliable

limitations of research into infradian rhythms - light therapy can produce headaches and eye strain

rohan 2009: recorded relapse rate of 46% over successive winters compared to 27% relapse rate in those having CBT

stages of sleep - ultradian rhythm

five distinct stages of sleep that span 90 minutes and continues throughout the course of the night, each of the stages is characterised by a different level of brainwave activity which can be monitored using an EEG

stage 1 of stages of sleep

light sleep where person can easily be woken, brain waves are alpha waves with high frequency short amplitude

stage 2 of stages of sleep

light sleep where person can easily be woken, alpha waves continue however there are occasional random changes in pattern called sleep spindles

stage 3 and 4 of stages of sleep

deep sleep/ slow wave sleep (SWS), brain waves are delta waves with low frequency and high amplitude, difficult to wake person

stage 5 of stages of sleep

REM sleep, body is paralysed but brain activity closely resembles that of an awake brain, brain waves are theta waves, eyes occasionally move around - dreams most likely to occur in this stage

strengths of research into ultradian rhythms - improved understanding of age-related changes in sleep

SWS reduces with age as growth hormone mainly produced during SWS, Van Cauter 2000: sleep deficit may explain issues in old age such as reduced alertness, to increase SWS relaxation and medication can be used - practical value of research

strengths of research into ultradian rhythms - control over extraneous variables - lab studies

researcher can exclude temporary variables such as noise or temperature that may affect sleep, cause and effect relationship can be established

limitations of research into ultradian rhythms - individual differences

tucker 2007: found large differences in ppts in terms of duration of each sleep stage especially stages 3 and 4, difficult to describe ‘normal sleep’ universally

limitations of research into ultradian rhythms - complicated machinery required

ppts sleep in a way which does not reflect their normal sleeping patterns, lacks mundane realism