Discuss research into infradian and/ or ultradian rhythms. (16 marks)
Infradian rhythms are biological rhythms that last longer than 24 hours they can last weekly,
monthly or annually. An example of an infradian rhythm is the female menstrual cycle,
which is regulated by hormones that either promote ovulation or stimulate the uterus for
fertilisation. Ovulation occurs roughly halfway through the cycle when oestrogen levels are
at their highest. After ovulation, progesterone levels increase in preparation for the possible
implantation of an embryo in the uterus.
Another example of an infradian rhythm is related to the seasons (exogenous zeitgeber).
SAD (seasonal affective disorder) , where some people become depressed and have lower
moods in the winter. Psychologists have hypothesised that melatonin, which is secreted by
the pineal gland during the night, is partly responsible. The lack of light during the winter
months results in a longer period of melatonin secretion, and this is thought to influence the
production of serotonin in the brain a chemical which has been linked to the depressive
symptoms.
Ultradian rhythms are biological rhythms that last less than 24hours an example of this is
the 5 stages of the sleep wake cycle. The first 4 stages of the cycle are NREM (non- rapid
eye movement) and the 5 stage is the REM stage (rapid eye movement). The cycle starts at
light sleep then progresses to deep sleep then into REM sleep. This cycle repeat itself about
every 90 minutes and on average a person might experience 5 full cycle per night.
A strength of infradian rhythms is there is research that suggests that the menstrual cycle
is, to some extent, governed by exogenous zeitgebers (external factors). For example,
Reinberg (1967) examined a woman who spent three months in a cave with only a small
lamp to provide light. He found that her menstrual cycle shortened from the usual 28 days
to 25.7 days. Therefore, these results suggest that the lack of light (an exogenous zeitgeber)
in the cave affected her menstrual cycle, and therefore this demonstrates the effect of
external factors on infradian rhythms.
Another strength of infradian rhythms is there is further evidence to suggest that exogenous
zeitgebers can affect them. For example, Russell, et al. (1980) found that female menstrual
cycles became synchronized with other females through odour exposure. In one study,
sweat samples from one group of women were rubbed onto the upper lip of another group.
Even though the two groups were separate, their menstrual cycles synchronised. This
suggests that the synchronisation of menstrual cycles can be affected by pheromones. Thus,
these findings indicate that external factors must be taken into consideration when
investigating infradian rhythms and that perhaps a more holistic approach should be taken,
as opposed to a reductionist approach that considers only endogenous influences.
A limitation of ultradian rhythms is the problem with studying sleep cycles is the individual
differences found in people. For example, 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). Moreover, the study was carried out in a lab setting, suggesting that the
differences in the sleep patterns were not because of situational factors, but only due to
biological differences in participants. Thus, this means that a range of factors contribute to
Infradian rhythms are biological rhythms that last longer than 24 hours they can last weekly,
monthly or annually. An example of an infradian rhythm is the female menstrual cycle,
which is regulated by hormones that either promote ovulation or stimulate the uterus for
fertilisation. Ovulation occurs roughly halfway through the cycle when oestrogen levels are
at their highest. After ovulation, progesterone levels increase in preparation for the possible
implantation of an embryo in the uterus.
Another example of an infradian rhythm is related to the seasons (exogenous zeitgeber).
SAD (seasonal affective disorder) , where some people become depressed and have lower
moods in the winter. Psychologists have hypothesised that melatonin, which is secreted by
the pineal gland during the night, is partly responsible. The lack of light during the winter
months results in a longer period of melatonin secretion, and this is thought to influence the
production of serotonin in the brain a chemical which has been linked to the depressive
symptoms.
Ultradian rhythms are biological rhythms that last less than 24hours an example of this is
the 5 stages of the sleep wake cycle. The first 4 stages of the cycle are NREM (non- rapid
eye movement) and the 5 stage is the REM stage (rapid eye movement). The cycle starts at
light sleep then progresses to deep sleep then into REM sleep. This cycle repeat itself about
every 90 minutes and on average a person might experience 5 full cycle per night.
A strength of infradian rhythms is there is research that suggests that the menstrual cycle
is, to some extent, governed by exogenous zeitgebers (external factors). For example,
Reinberg (1967) examined a woman who spent three months in a cave with only a small
lamp to provide light. He found that her menstrual cycle shortened from the usual 28 days
to 25.7 days. Therefore, these results suggest that the lack of light (an exogenous zeitgeber)
in the cave affected her menstrual cycle, and therefore this demonstrates the effect of
external factors on infradian rhythms.
Another strength of infradian rhythms is there is further evidence to suggest that exogenous
zeitgebers can affect them. For example, Russell, et al. (1980) found that female menstrual
cycles became synchronized with other females through odour exposure. In one study,
sweat samples from one group of women were rubbed onto the upper lip of another group.
Even though the two groups were separate, their menstrual cycles synchronised. This
suggests that the synchronisation of menstrual cycles can be affected by pheromones. Thus,
these findings indicate that external factors must be taken into consideration when
investigating infradian rhythms and that perhaps a more holistic approach should be taken,
as opposed to a reductionist approach that considers only endogenous influences.
A limitation of ultradian rhythms is the problem with studying sleep cycles is the individual
differences found in people. For example, 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). Moreover, the study was carried out in a lab setting, suggesting that the
differences in the sleep patterns were not because of situational factors, but only due to
biological differences in participants. Thus, this means that a range of factors contribute to
