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.
INFRADIAN rhythms have a period greater than 24 hours but less than 1 year.
- 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.
ULTRADIAN rhythms span a period less than 1 day
- 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.
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)
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)
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)
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)
SHIFTWORK (SHIFT LAG)
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)
SHIFTWORK (SHIFT LAG)
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.
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.
JET LAG - TRAVELLING EAST TO WEST
- 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.
STAYING UP LATE AND GETTING UP LATE
- 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)