rhythms

• Biological rhythms are distinct patterns or changes in behaviour in body activity or behaviour in response to cyclical periods
• Ultradian rhythms: Those that last less than a day, e.g. sleep wake cycle
• Stages of sleep, Stage 1 and 2 is known as the sleep escalator, with alpha waves at the start getting gradually longer and slower (theta), relatively easy to wake someone at this point

  Stage 3 and 4 deeper sleep, slower delta waves, more difficult to wake someone at this point.

  Stage 5, REM sleep. Body enters a state of paralysis, but brain activity massively spikes up, this stage is highly correlated to the experience of dreaming.
• Dermot & Kleitman

  Found that wave activity during sleep cycles with a set of participants followed a cyclical pattern.

  Also found that those who were awoken during the REM stage of sleep were more likely to report dreaming, providing evidence for REM being associated with dreaming
• Shapiro

  Ultra-marathon athletes have been found to spend more time in REM sleep, providing evidence for REM being important in physical recovery of the body

  Haider

  Studied individuals who had been brought into the hospital for drug overdose. They found that those individuals spent more time in REM sleep, suggesting it is important for mental recovery.
• Circadian rhythms

  Cycles that last approximately a day e.g. sleep wake cycle

  Found that the lowest body temperature was around 4am

  Melatonin release starts at 9:30pm

  Highest blood pressure is around 7am
• Infradian rhythms

  Rhythms that last more than 24 hours, e.g. Seasonally affective disorder, Menstrual cycle
• Endogenous pacemaker – internal body clock which maintains a regular cycle, and keeps biological rhythms to time. The endogenous pacemaker for the sleep wake cycle is the suprachiasmatic nucleus, (SCN), which is found in the hypothalamus in the optic chiasm of the optic nerves. It detects light, which causes it to inhibit melatonin production from the pineal gland, resulting in an inhibition of the sleep response.
• Exogenous zeitgeber – external cues which keep the biological rhythms to time. The primary exogenous zeitgeber for the sleep-wake cycle is light, but can also be influenced by meal times, other people and social cues. 
• Real-life application of studies into the sleep/wake cycle:

  Jet-lag and shift work.

  Office workers were split into two categories. One category was exposed to blue, artificial light, and the other category was exposed to natural light. It was found that the sleep/wake cycles of those in the natural light condition followed the changing times, whereas those in the artificial light condition, their sleep/wake cycles did not change. Showing that artificial light also had an effect on the sleep wake cycle, as well as natural light
• Chronotherapeutic, light therapy which has been found to reduce symptoms of affective disorders such as bipolar. 2/3 of bipolar sufferers reported a 50% lower inventory score after a course of light therapy.
• Golden hamsters with a Tau mutation had a sleep wake cycle of 20 hours

  Normal golden hamsters had a sleep wake cycle of 24 hours

  The SCNs of the two hamster types were switched, and it was found that the sleep-wake cycle timings also switched, providing evidence that the SCN is the endogenous pacemaker of the sleep-wake cycle

  HOWEVER, animal studies are difficult to extrapolate to humans as we are qualitatively different.
• One example of a circadian rhythms is the sleep/wake cycle which dictates when humans and animals should be asleep and awake. Light provides the primary input into this system, acting as the

  external cue for sleeping and waking. Light is first detected by the eye which then sends messages concerning the level of brightness to the suprachiasmatic nuclei (SCN). The SCN then uses this information

  to coordinate the activity of the entire circadian system. Sleeping and waking are also determined by homeostasis: when an individual has been awake for some time homeostasis tells the body that there is a

  need for sleep.
• There is research evidence to support the role of external cues on circadian rhythms. Siffre (1975) spent several extended periods underground to study the effects on his own biological rhythms. When he returned from an underground stay with no clocks or light he believed it to be mid-August when it was actually mid-September. These findings therefore support the role of external cues on circadian rhythms as the 24 hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was and leading to him thinking that fewer days had passed.
• However, it could be argued that such studies should not be generalised to all people as individual differences exist in relation to circadian rhythms. For example, studies have found that individual cycles can vary from 13 to 65 hours while research has also indicated that some people display a natural preference for going to bed early and rising early (known as ‘larks’) while others prefer to do the opposite (‘owls’). This therefore means that there may be innate individual differences in circadian rhythms, which suggests that researchers should acknowledge such differences during investigations.
• Infradian rhythms are a type of biological rhythm with a frequency of less than one cycle in 24 hours. One example of an infradian rhythm is the menstrual cycle in females which is governed by monthly

  changes in hormone levels which regulate ovulation. The cycle refers to the time between the first day of a woman’s period, when the womb lining is shed, to the day before her next period. The typical cycle takes approximately 28 days to complete (although between 24 – 35 days is considered normal).
• While the menstrual cycle is an endogenous system, there is research evidence which suggests that the menstrual cycle can be influenced by exogenous factors. In one study, samples of pheromones were gathered from 9 women at different stages of their menstrual cycle, from pads placed under the armpit.

  On day one pads from those at the start of the menstrual cycle were rubbed on the upper lip of the participants, on day two they were given a pad from the second day of the cycle and so on. It was found

  that 68% of the participants experienced changes to their cycle which brought them closer to their ‘donor’, therefore indicating that it is important to consider the effect of external factors when investigating

  infradian rhythms.
• Furthermore, there is research to suggest that infradian rhythms such as the menstrual cycle are also important regulators of behaviour. For example, Penton-Volk et al. (1999) found that woman expressed a preference for feminised faces at the least fertile stage of their menstrual cycle, and for a more masculine face at their most fertile point. These findings indicate that women’s sexual behaviour is motivated by their infradian rhythms, highlighting the importance of studying infradian rhythms in relation to human

  behaviour.
• Ultradian rhythms are a type of biological rhythm with a frequency of more than one cycle in 24 hours. One example of this is the sleep cycle- the different stages of sleep that we go through. Psychologists have identified five distinct stages of sleep that altogether span approximately 90 minutes, with this cycle continuing throughout the night. Stages 1 and are light sleep where a person is easily woken. Brainwave patterns start to become slower and more rhythmic. Stages 3 and 4 is deep sleep, where waves are slower still and it is difficult to wake someone at this point. Stage 5 is REM sleep where

  the body is paralysed yet brain activity speeds up significantly in a manner that resembles being awake. REM stands for rapid eye movement to reflect the fast, jerky movement of the eyes under the eyelids during this stage.
• There is research evidence to support the proposal of distinct sleep stages. One study monitored the sleep patterns of nine adults in a sleep lab. Brainwave activity was recorded on an EEG and the researchers controlled for the effects of caffeine and alcohol. REM activity was highly correlated with the experience of dreaming, brain activity varied according to how vivid the dreams were, and participants woken during dreaming reported very accurate recall of their dreams. These findings therefore suggest that REM sleep is

  an important component of the ultradian sleep cycle.
• However, a problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. Tucker et al. (2007) found significant differences between participants in

  terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is important to consider such differences during investigations into sleep cycles.
• Endogenous pacemakers (EP) are internal body clocks that regulate many of our biological rhythms. One example of this is the suprachiasmatic nucleus (SCN), a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain, which is influential in maintaining circadian rhythms such as the sleep/wake cycle. The SCN receives information about light directly from optic chiasm, and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
• There is research evidence from animal studies to support the role of endogenous pacemakers in the sleep/wake cycle. For example, in one study the SCN connections in the brains of 30 chipmunks were

  destroyed before they were returned to their natural habitat and observed for 80 days. It was found that the sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep). These findings therefore provide clear evidence for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
• However, a limitation of this study is that it raises significant ethical concerns. The animals were all exposed to harm through the intentional damaged inflicted to their SCNs, and this action then led to a greater risk of harm once returned to their natural environment as they were more open to attack from predators. While the findings of the study offer a clear indication of the role of EPs such as the SCN on the sleep/wake cycle, it could be argued that these findings do not justify the harm that was caused to the animals involve, particularly when the extent to which the findings can be generalised to humans is questionable.
• Social cues are also important exogenous zeitgebers: for example, infants often start with a seemingly random sleep/wake pattern but most follow a regular pattern by approximately 16 weeks. It is likely that the schedules imposed by parents in relation to mealtimes and bedtimes plays an important role in this process.
• There is research evidence to support the role of EZs on the sleep/wake cycle. For example, Siffre (1975) spent several extended periods underground to study the effects on his own biological rhythms. When he returned from an underground stay with no clocks or light he believed it to be mid-August when it was actually mid-September. These findings therefore support the role of EZs on circadian rhythms as the 24 hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was and leading to him thinking that fewer days had passed.
• However, it has been argued that the influence of EZs on the sleep wake cycle has been overstated. Miles et al (1977) gave an account of a young man who was blind from birth, with a circadian rhythm of

  24.9 hours. Despite exposure to social cues his sleep/wake cycle could not be adjusted. Furthermore, studies of individuals who live in the Arctic regions (where the sun does not set during summer months)

  show normal sleep patterns despite the prolonged exposure to light. Such examples therefore indicate that exogenous zeitgebers may sometimes have little effect on our sleep/wake pattern.