Lesson 12: Ultradian And Infradian Rhythms

Question 1

Ultradian rhythms

Answer 1

Ultradian rhythms span a period of less than 24 hours. An example is the five sleep stages. Human sleep follows a pattern alternating between Rapid Eye Movement (REM) sleep (which is stage five) and Non-Rapid Eye Movement (NREM) sleep (which consists of stages one, two, three and four). The cycle repeats itself every 90 minutes.

Each stage shows a distinct EEG pattern. As the person enters deep sleep, their brainwaves slow and their breathing and heart rate decreases. During the fifth stage (REM sleep), the EEG pattern resembles that of an awake person. It is during this stage that dreaming occurs.

Kleitman (1969) referred to the 90 minute cycle found during sleep as the Basic Rest Activity Cycle (BRAC). He suggested that this 90 minute cycle continues when we are awake. During the day, rather than moving through the sleep stages, we move progressively from a state of alertness into a state of physiological fatigue. Studies suggest that the human mind can focus for about 90 minutes, and towards the end of those 90 minutes the body begins to run out of resources, resulting in loss of concentration, fatigue and hunger.

Question 2

Advantages of Ultradian Rhythms

Answer 2

+ Ericsson et al. (2006) found support for the ultradian rhythms. They studied a group of elite violinists and found that among this group practise sessions were limited to 90 minutes at a time. Violinists frequently napped to recover from practise, with the best violinists napping more. The same pattern was found among athletics, chess players and writers. This fits with the BRAC.

Question 3

Disadvantages of Ultradian Rhythms

Answer 3

• Tucker et al. (2007) suggests that there are individual differences in ultradian rhythms which are biologically determined and may even be genetic in origin. Participants were studied over 11 consecutive days and nights in a laboratory environment. The researchers assessed sleep duration, time taken to fall asleep and the amount of time in each sleep stage. They found differences in all of these characteristics.

Question 4

Infradian Rhythms

Answer 4

Infradian rhythms span a period of longer than 24 hours; they may last weeks, months or even a year. One example of an infradian rhythm is the menstrual cycle, which lasts for about a month. There are considerable variations in the length of this cycle, with some women experiencing a 23 day cycle and others a 36 day cycle (Refinetti, 2006). The average is 28 days.

Hormones regulate the menstrual cycle. Ovulation occurs roughly halfway through the menstrual cycle, when oestrogen levels are at their peak, and usually lasts for 16-32 hours. After ovulation, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus.

Question 5

Advantages of Infradian Rhythms

Answer 5

+ Infradian rhythms can affect behaviour. Penton-Voak (1999) found that women express a preference for feminised male faces when choosing a partner for a long-term relationship. However, they showed a preference for masculinised faces during ovulation

Question 6

Disadvantages of Infradian Rhythms

Answer 6

• The menstrual cycle is not only governed by infradian rhythms. When several women of childbearing age live together, and do not take oral contraceptives, their menstrual cycles synchronise. In one study samples of sweat were collected from one group of women and rubbed onto the upper lip of another group of women, their menstrual cycles became synchronised. This suggests that the synchronisation is affected by pheromones. These are a chemical substance produced and released into the environment by an animal which
  affects the behaviour of others of the same species