Biological Rhythms - Circadian Rhythms

Question 1

What are Biological Rhythms?

Answer 1

Distinct patterns of change in body activity that conform to cyclical time period

Question 2

Circadian Rhythms

Answer 2

A specific type of body rhythm that occurs across 24hr period

e.g. sleep/wake cycles

Question 3

Biological Rhythms - Ultradian Rhythms

Answer 3

Occur many times during the day

Question 4

Biological Rhythms - Infradian Rhythms

Answer 4

longer than a day - some are circa annual rhythms e.g. seasonal affective disorder

Question 5

How are Biological Rhythms controlled?

Answer 5

Internal body clocks - endogenous pacemakers

External changes in environment - exogenous zeitgebers

Question 6

How is Sleep/Wake Cycle Controlled?

Answer 6

EZs - we feel drowsy at night and alert at day shows effect of daylight
EPS - biological clock left on its own devices w/o influence of external stimuli (free-running)

• Governed by suprachaismatic nucleus (SCN) that lies above the optic chaism which provides info from eyes about light (can reset the SCN)

Question 7

Siffre - demonstrated a free-running circadian rhythm of about 25 hours

Answer 7

French caver spent long periods in dark caves to examine effects of free-running rhythm - 2 months in 1962 and 6 months in the 1970s

• In each case study, Siffre’s free-running circadian rhythm settled down to about 25 hours
• Had a regular sleep and wake cycle

Question 8

Aschoff + Wever - found circadian rhythm of 24-25hrs

Answer 8

• Group of pps spent 4 weeks in WW2 bunker w/o natural light
• All (but 1 - circadian rhythm extended to 29 hours) had cycles of 24 - 25 hrs

Suggests natural sleep/wake cycle is longer than 24 hours but is entrained by exogenous zeitegebers (e.g. daylight hours, meal times etc.)

Question 9

Folkard et al (1985) - showed endogenous pacemakers are stronger tham exogenous zeitgebers

Answer 9

• Studied 12 ppl who lived in dark cave for 3 weeks going to bed at 11:45pm and up at 7:45am
• Over the course of study, clock speed up - days = 22hrs

Found only 1 pp adjusted to new regime
Suggests => existence of strong free-running circadian rhythm that can’t be easily overridden by changes in environment

Question 10

AO3: Practical Application to Shift Work

Answer 10

• Understanding of adverse consequences of desynchronisation
• Bovin et al (1996) found shift workers experience less concentration around 6am (circadian trough) increasing accidents
• Knutsson 2003 found shift workers being 3x more likely to have heart disease

Thus => research into sleep/wake cycle may have economic implications in managing shift work

Question 11

Counter to Practical Application to Shift Work

Answer 11

• Research is correlational - desynchronisation may not cause observe difficulties
• Solomon (1993) concluded high divorce rates in shift workers might be due to missing family events

Suggests => may not be biological factors that creates the adverse consequences associated with shift work

Question 12

AO3: Practical Application to Medical Treatment

Answer 12

• Circadian rhythms coordinate the body’s biological processes
• Has an effect on pharmocokinetics - how well drugs are absorbed + distributed in the body
  + chronotherapeutics - timing drugs for max effect
• Aspirin reduces heart attacks, which are more likely in the AM - found most effective taken at night (Bonten et al, 2015)

Shows => circadian rhythm research can increase the effectiveness of treatments, leading to medication guidelines

Question 13

AO3: Generalisation is difficult to make due to small samples + case studies

Answer 13

• Research tends to involve small groups of pps (e.g. Ashcoff + Wever) or 1 pp (Siffre)
• Pps may not represent wider pop. + limits meaningful generalisations
• Siffre observed internal clock was slower at 60 than when he was younger

Suggests => even when same person is involved, there are factors that may prevent general conclusions being drawn

Question 14

AO3: Poor control in Studies

Answer 14

• Pps still used artificial light e.g. Siffre used a lamp then he woke up (due to assumption it had no effect)
• However, Czeisler et al (1999) were able to adjust pps Cr from 22hrs to 28hrs using dim lighting

Thus => use of light may be a confounding variable in study as it interferes with biological clock

Question 15

AO3: Individual Differences

Answer 15

• Czeisler et al (1999) - individual cycles vary in some from 13-65hrs
• Duffy et al (2001) - revealed some have a anatural preference for going bed early (larks) or later (owls)
• Also, age diffs. in sleep/wake patterns