Biopsych: Biological Rhythms

Question 1

What are biological rhythms?

Answer 1

A natural event that recurs on a regular basis, cyclically. E.g. the menstrual cycle, the sleep/wake cycle or the daily rising and falling of your temp.

Question 2

How are these rhythms controlled?

Answer 2

• environmental cues - suggests that rhythms are controlled and reset by environmental factors, e.g. light, temp and food availability. These are exogenous zeitgebers (‘time givers’)
  —> however, squirrels kept in labs with constant conditions still prepare for hibernations as winter approaches in the outside world, by putting on weight and decreasing body temp- suggesting it is more complicated
• if rhythms are maintained in absence of environmental stimulus of ‘cues’ then there must be some kind of internal clock that regulates biological rhythms in the absence of zeitgebers. These internal clocks are called endogenous pacemakers

Question 3

What are circadian rhythms?

Answer 3

‘About a day’ - rhythms occur over 24 hours. E.g. many hormones and neurotransmitters show similar circadian variation in activity
- over 100 bodily processes linked to the 24H periods (nocturnal, sleep/wake cycle, etc)

Question 4

How is the sleep/wake cycle controlled?

Answer 4

• Exogenous zeitgebers: light (e.g. day and night)
• endogenous pacemakers: Suprachiasmatic nucleus (SCN) - bundle of nerve fibres located in the brain above the optic chiasm which provided info from the eye, stimulant pineal gland to release melatonin
• EZ and EP interact - light resents SCN

Question 5

What is the Suprachiasmatic nucleus (SCN)?

Answer 5

A group of neurones in the hypothalamus. These neurones have their own regular rhythms of activity. The SCN is the most important endogenous pacemaker and in turn controls the pineal gland and releases melatonin

Question 6

What is the pineal gland?

Answer 6

A small structure in the brain that secretes the hormone melatonin, which in turn regulates many of our biological rhythms. Controlled by SCN.

Question 7

What is the process of the sleep/wake cycle?

Answer 7

1. Light - comes through eyelids (EZ)
2. Eye - photosensitive receptors transfer info as an electronic pulse to…
3. Optic nerve - transmits info to…
4. SCN - the main EP for the cycle. Sends message to…
5. Pineal gland - controls melatonin production (when melatonin is present, we are sleepy)
6. Melatonin prohibited - so we wake up (when melatonin stops, we wake)

Question 8

What’s some research into the individual differences of people in for sleep/wake cycles?

Answer 8

• Czeisler found that individual s/w cycles can vary, sometimes from between 13-65 hours
• Duffy also identified that some people prefer to get up earlier (larks) and some people go to bed later (owls). Owlishness and larkishness changes with age as well.
• Siffre found that as he go older, his free-running rhythm lengthened from around 25-30 hours to 48 hours

Question 9

What was Michel Siffres cave study?

Answer 9

In 1962, Siffre spent 2 months living in total isolation in a subterranean cave, without any acces to technology, clock, calendar or sun. Sleeping and eating only when his body told him to. His goal was to discover how the natural rhythms of human life would be affected by living ‘beyond time’

Question 10

What did Siffre find?

Answer 10

After 61 days, he resurfaced on the 14th sept, thinking it was 20th Aug. The length of his time awake each day varied in length, from as little as 6 hours to 40 hours. He settled into a 24 hour and 30 minute cycle.

Question 11

What was Siffres second attempt?

Answer 11

He spent 6 months in a cave in Texas. His natural circadian rhythm settled to just above 24 hours (25-30 hours)
- on his final stay in 1999, he found his body clock was more slow compared to being young, sometimes reaching 48 hours.
This supports that EPs exert an influence on circadian rhythms

Question 12

How did Aschoff and Rutger support this Siffres study?

Answer 12

Put ptps in a WWII bunker with no lnatural light for 4 weeks, found a s/w cycle of 25-27 (apart from one 29) hours - suggests EPs control s/w cycle in the absence of light cues

Question 13

What does Folkard find that shows the strength of circadian rhythms?

Answer 13

He manipulated the clock to 22 hours a day to 12 isolated ptps in a dark cave for 3 weeks with no natural light - found none of the ptps could adjust comfortably to the pace of the 22 hour clock. As well as this, questions the extent to which it can be overridden by EZs.

Question 14

What’s some limitations to Siffres study?

Answer 14

• population validity is low
• control is not perfect - Siffre had access to artificial light (may have affect the rhythm)
  —> Czeisler found you can use dim light to adjust ptps circadian rhythm form 22 to 28 hours, so the lamp may have been a confounding variable

Question 15

What are some practical applications from this theory?

Answer 15

• shift work - knowledge of circadian troughs (Boivin) and desynchronisation has helped inform workplaces of how to avoid accidents caused by these (e.g. Chernobyl)
  —> research has helped reduce stress caused by night shifts that leads to heart disease (Knutson) by recommending fixed shifts rather than rotating, or phase delay rather than phase advance, where shifts have to rotate

Question 16

What are infradian rhythms?

Answer 16

Longer than one day
- control of these rhythms must involve both EPs and EZs (e.g. menstrual cycle, hibernation, etc)

Question 17

How is the menstrual cycle a infradian rhythm?

Answer 17

• starts with the first day of period, where womb sheds its lining and ends day before next period
• typically takes 28 day s
• rising Oestrogen levels cause ovary to release an egg (ovulation). Then progesterone causes the womb longing to grow thicker, readying the body for pregnancy.
• if pregnancy doesn’t occur, womb lining is discarded (menstruation)

Question 18

What was McClintocks sweaty lip ladies study?

Answer 18

• 29 women with irregular periods. Gathered armpit sweat with pheromones from 9 of the women. Pads with sweat rubbed on the upper lip of other women.
• 68% of women experienced changes to cycle that brought them more in line with the cycles of their sweat donor - entrainment occurred.
• Menstrual synchrony through entrainment may have evolutionary value. —> Advantages to fall pregnant at same time, as newborns can be cared for collectively (e.g. breast feeding) and therefore more likely to survive.

Question 19

What were some problems with McClintocks study?

Answer 19

• validity has been questioned (Schank 2004) as ovulating at the same time could mean competing for best partner and their resources, so avoiding synchrony would be adaptive.
• Confounding variables: many factors may change the cycle (e.g. stress, diet, exercise), so changes that occurred could of been by chance
• Small samples and reliance of self reports on own cycles
• Failure to replicate- Trevathen (1993) + others have failed to find evidence of menstrual synchrony in all female samples

Question 20

What are seasonal affective disorders?

Answer 20

• symptoms of depression, experienced with a seasonal pattern of onset (‘winter blues’)
• circannual rhythm - yearly
• attributed to longer hours of darkness during winter
• melatonin secreted for longer as night is longer. This affects production of serotonin, causing onset of depressive symptoms.

Question 21

What are ultradian rhythms?

Answer 21

• less than a days length
• e.g. during a nights sleep, we move systematically through different phrases of sleep. One cycle takes approx 90 minutes.
• Control of this cycle involves a network of centres in the brain communicating through a variety of neurotransmitters.
• Key elements are the SCN and the Pineal Gland.

Question 22

What is stage 1 of the sleep cycle?

Answer 22

4-5% —> light sleep, muscle activity slows down with the occasional muscle twitching

Question 23

What is stage 2 of the sleep cycle

Answer 23

45-55% —>breathing pattern and heart rate slows, slight decrease in body temp

Question 24

What is stage 3 of the sleep cycle?

Answer 24

4-6% —> deep sleep begins, brain begins to generate slow delta waves

Question 25

What’s stage 4 of the sleep cycle?

Answer 25

12-15% —> very deep sleep. Rhythmic breathing, limited muscle activity, brain produced delta waves

Question 26

What is stage 5 of the sleep cycle?

Answer 26

20-25% —> rapid eye movement (REM). Brainwaves speed up and dreaming occurs and muscles relax and heart rate increases. Breathing is rapid and shallow.

Question 27

What is some of the evidence supporting distinct stages of sleep?

Answer 27

-Dement and Kleitman monitoring brainwave activity of 9 ptps using EEG. REM activity highly correlated with dreaming.
- Replications have found similar findings; REM is an important component of the cycle

Question 28

Why did Kleitman suggest a 90 minute cycle during waking hours as well as sleep?

Answer 28

• BRAC (Basic Rest Activity Cycle) - alertness, then fatigue in a 90 minute rhythm
• Ericsson (1993) supported this: best violinists tended to practise for 3 sessions a day, each for no longer than 90 minutes with a break in between to recharge.

Question 29

What does the case study of Randy Gardener found that stages of sleep may be more important than others and the flexibility of ultradian rhythms?

Answer 29

Randy remained awake for 264 hours.
- while he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with a massive sleep loss.
- After this experience, Randy slept for just 15 hours and several nights, he recovered only 25% of his lost sleep. Interestingly, he recovered 70% of stage 4 sleep, 50% of REM and very little of the others
- These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this Ultraradian rhythm.