Biological Rhythms

Physiological psychology

Circadian, Infradian, Ultradian biological rhythms

Endogenous pace makers and exogenous zeitgebers

Consequences of disrupting rhytms

HideShow resource information
  • Created by: Marie
  • Created on: 25-05-09 22:13

CIRCADIAN Rhythms last for 24 hours.

  • Endogenous evidence - from isolation studies, e.g. SIFFRE (1975) lived in a cave for 6 months; his rhythm varied between 24 and 48 hours.
  • A02: However, in isolation studies participants are not isolated from artificial light; therefore are not actually testing the free running cycle.
  • A02: Research suggest individual differences in sleep-wake cycle length (Czeislet et al., 1999) and cycle onset (Duffy et al., 2000)
  • Exogenous zeitgebers - Bright light resets circadian rhythms; dim light may have an effect too (WEVER et al., 1983)
  • A02: exogenous zeitgebers are important because they enable circadian rhythms to synchronize with the environment.

Temperature cycle - this is highest as 4pm; certain behaviours vary with the temperature e.g. memory (FOLKARD et al., 1977)
A02: However... temperature rhythms is differnent from sleep-wake rhythm, suggesting more than one biological clock.
A02: Applications include ... chronotherapy and the importance of timing in medical tests.

1 of 11

INFRADIAN rhythms have a period greater than 24 hours but less than 1 year.

Monthly cycles:

  • The human menstrual cycle is on average 29.5 days
  • There is a male cycle affecting temperature and mood which lasts 20 days (EMPSON, 1977)
  • A02: Research support - synchronisation of menstrual cycles in women living together, i.e. influence of exogenous zeitgebers - social cues transmitted through pheromones (RUSSEL et al., 1980)
  • A02: However: despite the implicatoins that a pheromone is involved in this process, it has yet to be isolate.

Seasonal affective disorder:

  • Sufferers are depressed in winter
  • Melatonin (related to depression) is higher in winter
  • A02: Applications of this research include... using the understanding of SAD to develop effective therapy disorders such as phototherapy.
2 of 11

ULTRADIAN rhythms span a period less than 1 day

Sleep stages:

  • NREM sleep: stages 1 and 2 are relaxed; stages 3 and 4 are slow-wave-sleep (SWS - growth hormone released)
  • REM sleep: dreams, neurotransmitters made.
  • A02: However... dreams are not exclusively linked to REM sleep; it is possible to explain dreaming in terms of a psychological rather than neurological function.
  • A02: A limitation of this research is that... sleep stages are recorded in artificial laboratory studies.

Basic rest-activity cycle (BRAC)

  • FRIEDMAN and FISHER (1967) gave evidence of cyclic eating and drinking behaviour.
  • A02: Research support: BRAC is generally support by research studies, e.g. GRAU et al. (1995), who confirmed the existence of an ultradian rhythm in motor activity in humans.
3 of 11


An endogenous pacemaker is an internal biological clock that controls an organism's circadian rhythms

A01: Biological Clock

  • This is created by interactions between proteins CLOCK and CYCLE, and PER and TIM.
  • They work in a feedback loop.

A02: Advantages of the biological clock - Without one, an animal may have irregular patterns of activity that may be life-threatening.

A02: Disadvantage - Rhythms may not change as rapidly as we need (e.g. effects of shift work, jet lag)

4 of 11


A01: Suprachiasmatic Nucleus (SCN)

  • This is found in the hypothalamus and obtains information about light from the optic nerve.
  • It depends on light to synchronise the biological clock with the cycles of light and dark in the outside world.

A02: Evidence for the importance of the SCN

  • If the SCN is damaged, the animal no longer responds to environmental cues, e.g. research with mutant hamsters (MORGAN, 1995)
  • Destruction of the SCN in chipmunks led to increased activity at night and a greater risk of predation (DeCOURSEY et al., 2000)
5 of 11


A01: Pineal Gland

  • The pineal gland responds when light increases by inhibiting the production of melatonin (which is responsible for inducing sleep).
  • It is an especially important pacemaker in birds and reptiles (the third eye)

A02: The importance of the pineal gland is shown by... the fact that after the removal of the pineal gland, animal may continue to produce melatonin (MOYER et al., 1997)

A02: Research support

  • Chickens wake and become active as dawn breaks (when external light levels rise and melatonin levels fall) (BINKLEY, 1979)
6 of 11

Exogenous Zeitgebers - These are environmental cues that reset the biological clock so that it matches local conditions

A01: SOCIAL CUES: These include meal times and normal bed times. Until recently these were thought to be the main human zeitgeber.
A02: However: Social cues are important only in social animals; the purpose is to provide a means of regulatin social behaviours.

A01: LIGHT: This is the dominant zeitgeber in humans. Bright light suppresses melatonin, but even dim lighting may have an effect (WEVER et al., 1983)
A02: Importance of light as a zeitgeber:
- It ensures activity during daylight and inactivity during darkness
- Blind people experience difficulty maintaining a 24-hour cycle, e.g. one man had a rhythm of 24.9 hours despite clocks and other social cues (MILES et al., 1977)

A01: Temperature: Temperature can also entrain biological rhythms; it causes leaves to drop and hibernation to commence.
A02: However... it is possible to overide the biological system - people told to wake up earlier have raised hormone levels just before designated time - a case of mind over matter (BORN et al., 1999)

7 of 11


Disruption of the 24 hour circadian rhythm in night workers leads to circadian 'trough' in alertness at about 6am (BOIVIN et al., 1966)

A01: Partial Sleep Deprivations

  • Sleeping during the days is difficult because of daytime noises and light.
  • Sleep is typically 1-2 hours shorter (TILLEY and WILKINSON, 1982)
  • REM is particularly affected.


  • Individual differences: in how people cope with shift work; those whose circadian rhythms are slowest to adapt cope better (REINBERG et al., 1984)
  • Desynchronization of different rhythms may cause problems: The sleep-wake cycle is quicker to adjust (48 hours) (YAMAZAKI et al., 2000)
  • Rotation shifts have the most harmful effects: these can be minimised by rotating shifts in one direction i.e. phase delay (CZEISLER et al., 1982)
8 of 11


A01: Poor quality sleep

  • Quantity and quality of sleep are affected
  • Sleep deficit and fatigue then affect work performance

A01: Heat disease

Shift Workers are three times more likely to develop heart disease (KSNUTSSON, 1982)

A02: Although... dim lighting does not appear to reset the biological clock, bright lights can mimic the effect of daylight and reset the biological clock within 3 days (CZEISLER et al., 1986)

A02: An applications of this research is shown by... CZEISLER et al., (1982), who gave advice to a US company: worker satisfaction and output then increased.

9 of 11


A01: Jet lag is cause by the sudden creation of a large discrepancy between the internal clock and external world.

A02: However... other factors (e.g. anxiety, alcohol, low oxygen in cabin air) might also contribute to the harmful effects if jet lag.

A02: Why is jet lag harmful? - Jet lag cause desynchronization of body clocks throughout the body.

A02: Research support: A BRE meta-study (2001) found evidence of reduced alertness and concentration related to jet lag.

A02: However, findings on mental performance were inconsistent suggesting the role of motivation or some other confounding factor.

A01: Non-adaptive: The biological clock is not equipped to deal with sudden changes of time zone.

10 of 11


  • Adjustment is more difficult when flying west to east (i.e. phase advance) because disruption of the circadian rhythm is more dramatic.
  • Baseball teams won 37% of games when travelling west to east (phase advance) and 44% when travelling east to west (RECHT et al., 1995)

A02: However: Studies of the effects of jet lag on athletes have been inconclusive, suggesting performance is not adversely affected provided motivation remains high.


  • This subverts established circadian rhythms
  • Sleeping longer has effects similar to sleeping less

A02: Research support

Participants slept either 9pm - 5am or 3am to 11am. Both groups showed reduced alertness and vigilance (TAUB and BERGER, 1976)

11 of 11


No comments have yet been made

Similar Psychology resources:

See all Psychology resources »