Biological Rhythms: Ultradian & Infradian Flashcards
Infradian:
A type of biological rhythm with a frequency of less than one cycle in 24 hours, such as menstruation and seasonal affective disorder.
Ultradian rhythm:
A type of biological rhythm with a frequency of more that one cycle in 24 hours, such as the stages of sleep.
IR: Menstrual Cycle
- 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, the women’s period when the lining is shed to the day before her next period.
- This takes approximately 28 days (between 24-35 days)
IR: Menstrual Cycle Hormones
- Rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation).
- After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy.
- If pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (menstrual flow).
IR Menstrual Cycle: Research Study
- Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors.
- Kathleen Stern and Martha McClintock (1998) demonstrated how menstrual cycles may synchronise as a result of female pheromones.
- McC involved 29 women with a history of irregular periods. Samples of pheromones were gathered from 9 of the women at different stages of the MC using a cotton pad under their armpit.
- The pads were worn for at least 8 hours then were treated with alcohol and frozen and were rubbed on the upper lip of the other participants.
- On day 1, pads from the start of the menstrual cycle were applied to all 20 women, on day 2 they were given a pad from the 2nd day.
- McC found that 68% of women experienced changes to their cycle with brought them closer to the cycle of their ‘odour donor’.
SAD: Seasonal Affective Disorder
- A depressive disorder has a seasonal pattern of onset and the main symptoms are persistent low mood alongside a general lack of activity and interest in life.
- SAD is often referred to as the winter blues as the symptoms are triggered during the winter months as daylight hours becomes shorter.
- SAD is a particular type of infradian rhythm called a circannual rhythm (yearly).
- This can also be considered a circadian rhythm as SAD experience may be due to disruption of the sleep/wake cycle and this could be due to the prolonged periods of darkness in water.
SAD: Melatonin
- Psychologists have hypothesised that melatonin is implicated in the cause of SAD.
- During the night, the pineal gland secretes melatonin until dawn when there is an increase in light.
- During winter, the lack of light in the morning means this secretion process continues for longer.
- This is thought to have a knock-on effect on the production of serotonin in the brain.
- This is a chemical that has been linked to the onset of depressive symptoms.
UR: Sleep Stages 1-2
Stage 1 and 2: Light sleep where the person may be easily woken. At the beginning of sleep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even slower as sleep becomes deeper (theta waves).
UR: Sleep Stages 3-5
Stages 3 and 4: Involve delta wave which are slower still and have a greater amplitude than earlier wave patterns. This is deep sleep or slow wave sleep and it is difficult to rouse someone at this point.
Stage 5, REM sleep: the body is paralysed yet brain activity speeds up significantly in a manner that resembled the awake brain. REM stands for rapid eye movement, to denote the fast, jerky activity of the eyes under the eyelids at this point. Research has suggested that REM activity during sleep is highly correlated with the experience of dreaming.
E: Evolutionary Basis of the MC
- Menstrual synchrony, shown in the McClintock is thought to have evolutionary value.
- For our ancestors it may have been advantageous for females to menstruate together and fall pregnant at the same time.
- This meant that newborns could be cared for collectively, increasing the chances of offspring’s survival.
- This idea was questioned by Jeffrey Schank (2004) argued that if there were too many females cycling together, this would produce competition for the highest quality males.
- This lowers the fitness of any potential offspring, this means that avoiding synchrony appears to be the better evolutionary strategy.
E: Methodological Limitation in Synchronisation Studies
- They argue that are many factors that may effect change in a woman’s menstrual cycle, including stress, changes in diet and exercise. These may act as confounding variables.
- This means that any supposed pattern of synchronisation is no more than would have been expected to occur by chance.
- Research typically involves small samples of women and relies on participants self-reporting on the onset of their own cycle.
- Also other studies (Trevathan et al.1993) failed to find any evidence of menstrual synchrony in all-female samples.
E: Support for the Idea of Distinct Stages in Sleep
- William Dement and Nathaniel Kleitman (1957) monitored the sleep patterns of nine adult participants in a sleep lab.
- Brainwave activity was recorded on an EEG and the researchers controlled for the effects of caffeine and alcohol.
- REM was highly correlated with the experience of dreaming, brain activity varied according to how vivid dreams were and participants woken during dreaming reported very accurate recall of their dreams.
- Replications have noted similar findings, criticised the small sample size. Still suggests that REM sleep is an important component of the ultradian sleep cycle.
E: Animal Studies
- Much of the knowledge on the effects of pheromones on behaviour is derived from animal studies. The role of pheromones in animal sexual selection is well-documented.
- Sea urchins released pheromones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously.
- In contrast, evidence for human behaviour remains speculative and inconclusive.
Practical Application: SAD
- One of the most effective treatments for SAD is phototherapy.
- This is a light box that simulates very strong light in the morning and evening.
- It is thought to reset melatonin levels in people with SAD, relieving symptoms in up of 60% of individuals (Eastman et.al 1998)
- However, the same study recorded a placebo effect of 30% using a sham negative ion generator. Participants were told it was another form of treatement.
- Casts doubt on the influence of phototherapy.
