Biological Rhythms

Question 1

Infradian rhythms

Answer 1

Biological rhythms which happen over a time period greater than 24 hours (monthly or yearly)

Question 2

Examples of infradian rhythms

Answer 2

Menstrual cycle (28 days on average)
Seasonal affective disorder (SAD) (yearly cycle)

Question 3

Ultradian rhythms

Answer 3

Biological rhythms that happen more than once over a 24 hour period

Question 4

Examples of ultradian rhythms

Answer 4

Pulse
Heart rate
Blood circulation
Sleep stages

Question 5

Circadian rhythms

Answer 5

Biological rhythms that happen over a period of about 24 hours

Question 6

Examples of circadian rhythms

Answer 6

The sleep-wake cycle
Daily fluctuations in heart rate, blood pressure, blood sugar and body temperature

Question 7

Siffre’s cave study (1975)

Answer 7

• Spent several extended periods of time in a cave
• He was deprived of exposure to natural light and sound with access to adequate food and drink for two months in 1962
• Siffre resurfaced mid-September 1962 but he believed it to be mid-August
• His biological rhythm was just over the usual 24 hours at about 25 hours
• He fell asleep and woke up on a regular schedule when he felt it was appropriate to do so

Question 8

Aschoff and Wever (1976)

Answer 8

• Convinced a group of 12 participants to spend 4 weeks in a WW2 bunker, deprived of natural light
• All but one of the participants had a sleep-wake cycle of 24-25 hours

Question 9

Simon Folkard (1985)

Answer 9

• Studied a group of 12 people who agreed to live in a dark cave for 3 weeks
• They went to bed when the clock said 11:45 and woke up when it said 7:45
• Over the course of the study, the researchers gradually sped up the clock (without the participants knowing) so that an apparent 24 hour day lasted 22 hours
• Only one of the participants were able to comfortably adjust to the new routine
• Suggests our natural circadian rhythm cannot easily be overridden by exogenous zeitgebers

Question 10

What is the endogenous pacemaker for sleep?

Answer 10

The suprachiasmatic nucleus (SCN) in the hypothalamus

Question 11

What hormone does the SCN control?

Answer 11

Melatonin

Question 12

Light and the SCN

Answer 12

If there is less light, more melatonin is produced
If there is more light, less melatonin is produced

Question 13

What two components work together to control the sleep-wake cycle?

Answer 13

The endogenous pacemaker and exogenous zeitgeber

Question 14

Endogenous pacemakers

Answer 14

Internal factors controlling natural rhythms

Question 15

Menaker (1978)

Answer 15

• Bred a strain of hamsters so they had abnormal circadian rhythms of 20 hours as opposed to 24 hours
• SCN neurons from these hamsters were then transplanted into the brains of normal hamsters
• The normal hamsters displayed the same abnormal circadian rhythm
• SCN neurons from normal hamsters were planted into the brains of abnormal hamsters and these abnormal hamsters changed to a circadian pattern of 24 hours
• This shows the importance of the SCN in regulating circadian rhythms

Question 16

Strength of Menaker’s study

Answer 16

Scientific and controlled

Question 17

Limitations of Menaker’s study

Answer 17

Cannot generalise from animals to humans

Question 18

Strength of Siffre’s cave study

Answer 18

Controlled environment so could be replicated

Question 19

Limitations of Siffre’s cave study

Answer 19

Ecological validity - most of us do not live underground
Cannot generalise from a case study

Question 20

Czeisler (1982) method

Answer 20

• 85 male workers from a Utah chemical plant on a rotating shift pattern and a control group of 68 male workers on non-rotating day shifts and swing shifts
• The rotating shift pattern was three 8 hour shifts (12am-8am, 4pm-12am and 8am-4pm)
• 33 workers were on the normal cycle of shift change every 7 days and 52 workers changed shifts every 21 days.
• Productivity was analysed after 9 months and the workers completed self- reposts on sleep, health and shift preferences

Question 21

Czeisler (1982) results

Answer 21

Workers on rotating shifts reported more sleeping problems. The delayed shift change reduced these issues and respondents did prefer it. Productivity increased and staff turnover decreased.

Question 22

Czeisler (1982) conclusion

Answer 22

Shift patterns that rotate by phase delay with an extended interval between each rotation seem to suit the human circadian rhythm better and reduce sleep issues. A 21 day cycle does have implications for social and family lifestyles

Question 23

Strength of Czeisler’s study

Answer 23

Practical implications

Question 24

Limitations of Czeisler’s study

Answer 24

Issues with self report
Cannot generalise to other types of shift work

Question 25

Limitations of research on biological rhythms

Answer 25

• Cannot extrapolate results from animal studies to humans
• Ethical concerns if research involves sleep deprivation
• Individual differences
• Difficult to separate biological, environmental and social factors

Question 26

Effects of aging - Siffre (1999)

Answer 26

Siffre found that his body clock ticked more slowly compared to a young man (he was 60 at this point) sometimes stretching his circadian rhythm to 48 hours.