Circadian Rhythms

Question 1

What is a circadian rhythm?

Answer 1

A rhythm with 24 hours periodicity

Question 2

What is the main circadian rhythm?

Answer 2

The sleep wake cycle

Question 3

Name 2 other examples of circadian rhythms

Answer 3

Body temperature and hormones

Question 4

What 2 exogenous factors affect the sleep wake cycle?

Answer 4

Light and time

Question 5

For the sleep wake cycle, what is the main study supporting the internal clock?

Answer 5

Siffre (1975)

Question 6

Outline Siffre (1975)

Answer 6

Spent 6 months in a cave without light or time cues, he quickly settled into a regular 24.9 hour rhythm so shows a consistent rhythm (but need exogenous zeitgebers to get rhythms to fit with the natural 24 hour day)

Question 7

Name a positive about Siffre (1975)

Answer 7

Supported by Aschoff & Wever (1976) who put ppts in an underground WW2 bunker, most circadian rhythms between 24-25 hours but some 29 hours. This shows they still operate in the absence of exogenous zeitgebers

Question 8

Name 2 negatives about Siffre (1975)

Answer 8

1) Case study so generalisability

2) Cave is not a real-life setting and temperature cannot be controlled which could have affected them

Question 9

For the sleep wake cycle, what is the main study supporting exogenous zeitgebers?

Answer 9

Folkard (1985)

Question 10

Outline Folkard (1985)

Answer 10

12 people in a cave for 3 weeks who agreed to go to bed when the clock indicated 11:45pm and get up 7:45am. Initially the clock ran normally, but it gradually quickened so it indicated 24 hours had passed but only 22 hours had actually passed. At first. the rhythms matched the clock but as it quickened, they ceased to match and continued to follow the 24 hour cycle (except for 1 ppt). So it suggests rhythms are only guided to a limited extent by exogenous zeitgebers

Question 11

For the sleep wake cycle, explain 2 negative points

Answer 11

1) In the research studies, isolated from exogenous zeitgebers but not from artificial light as thought that it has no effect, but Czeisler (1999) altered rhythms to 22 and 28 hours by using dim lighting
2) There are individual differences - cycle length and onset. Czeisler (1999) found rhythms can vary from 13 to 65 hours and individuals appear to be innately different in terms of when they peak (e.g. morning and evening people)

Question 12

Outline Czeisler (1999)

Answer 12

Altered rhythms to 22 and 28 hours by using dim lighting

Question 13

Outline the core body temperature cycle

Answer 13

Lowest at 4:30am and highest at around 6:00pm

Question 14

For core body temperature, what is the main study?

Answer 14

Folkard (1977)

Question 15

Outline Folkard (1977)

Answer 15

Investigated how body temperature affects cognitive performance, asked 12-13 year olds to read stories at either 9am or 3pm. After a week, found the afternoon group (higher temp) showed superior recall and comprehension suggesting long-term recall is best when temp is at its highest

Question 16

Explain 2 positive points about Folkard (1977)

Answer 16

1) Supported by Gupta (1991) who found that performance on IQ tests was best at 7pm compared with 9am or 2pm
2) Real-world application

Question 17

Explain a negative point about Folkard (1977)

Answer 17

Cause or correlation? Hord & Thompson (1983) tested cognitive performance in the field rather than the lab situation and they didn’t find any correlation

Question 18

Outline Meddis (1975)

Answer 18

Individual differences - the average is 7.8hours but many can survive on less

Question 19

Outline Miles (1977)

Answer 19

Supports Siffre - case study of a totally blind man who had a 24.9 hour rhythm. He had to take stimulants and sedatives to fit with the natural 24 hour day

Question 20

What does Meddis (1975) show?

Answer 20

Individual differences in sleep wake cycle

Question 21

What does Miles (1977) show?

Answer 21

Supports Siffre in the internal clock, but also that need exogenous zeitgebers to fit in with the 24 hour day

Question 22

What does Folkard (1996) show?

Answer 22

The influence of zeitgebers or individual differences

Question 23

Outline Folkard (1996)

Answer 23

Uni volunteer Katie Aldcroft who was put in a lightproof room with no zeitgebers for 25 days. She very quickly went on to a 30 hour cycle and reported feeling very fit, healthy and alert

Question 24

2 disadvantages of Folkard (1996)

Answer 24

1) It is a case study so generalisability

2) It may just be down to huge individual differences in our rhythms

Question 25

4 IDA points for circadian rhythms?

Answer 25

1) Biologically based despite explaining human behaviour which is more complex as we can override biologically determined behaviours (waking up and going to bed)
2) Not always possible to override biology (Miles)
3) Determinist (misleading) - states set by endogenous pacemaker but some flexibility (the one ppt in Folkard (1985) who managed to keep the 22 hour rhythm)
4) Real-world application - Chrono therapeutics and studying

Question 26

What is Chrono therapeutics?

Answer 26

How timing affects drugs