Biopsychology
Ultradian & Infradian Rhythms
Biological rhythms are cyclical patterns in biological systems. Ultradian rhythms last for a
period less than 24 hours; for example, sleep patterns. They tend to occur more than once over
24 hours. This cycle alternates between REM (rapid eye movement) and NREM (non-rapid eye
movement), and consists of five stages, starting at light sleep, progressing into deep sleep and
then into REM sleep. This cycle repeats itself about every 90 minutes–on average, a person
might experience five full cycles per night.
However, individual differences in humans may cause difficulties when studying the sleep cycle.
Tucker et al. found significant differences between participants in terms of duration of each
sleep stage, particularly stages 3 and 4 (deep sleep NREM, the stages preceding REM.) This
study was carried out in a controlled lab setting, meaning the differences in sleep patterns could
not be attributed to extraneous variables, but rather only to the biological factors/differences
between participants. Therefore, an idiographic approach should be conducted regarding
research into ultradian rhythms, rather than a nomothetic approach that generates general laws;
hence, accounting for differences between individuals.
Infradian rhythms are biological rhythms that last a period longer than 24 hours; they may be
weekly, monthly or yearly. A monthly infradian rhythm is the menstrual cycle, which is regulated
by hormones that either promote ovulation or stimulate the uterus for fertilisation. Ovulation
occurs halfway through the cycle, when oestrogen levels are highest, and usually lasts 16-32
hours. After ovulation, progesterone levels increase, ready for possible embryo implantation.
Whilst one may infer that infradian rhythms are governed by internal factors, research suggests
that the menstrual cycle is, to some extent, governed by exogenous zeitgebers. Reinberg
(1967) examined a woman who had spent three months in a cave with only a small lamp to
provide light; Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7
days. Lack of light (an exogenous zeitgeber) in the cave impacted her menstrual cycle,
therefore demonstrating the effect of external factors on infradian rhythms.
There is further evidence to suggest that exogenous zeitgebers impact infradian rhythms.
Russel et al (1980) found that menstrual cycles became synchronised 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. Despite these two groups being separate, their menstrual
cycles synchronised.
This therefore suggests that the synchronisation of menstrual cycles can be affected by
pheromones, indicating that external factors and exogenous zeitgebers should be taken into
account when investigating infradian rhythms. Perhaps a more holistic approach should be
taken, rather than a reductionist approach that considers only endogenous influences.
, Circadian Rhythms
Lasts 24 hrs. Sleep/wake cycle; light provides primary input, acting as external cues (exogenous
zeitgebers).
Siffre – stayed in a cave for 2 months. Absence of exogenous zeitgebers significantly impacted
his circadian rhythm; when surfacing, he believed the date to be a month earlier than it was.
Hemispheric Lateralisation
Hemispheric lateralisation refers to the idea that the two hemispheres of the brain are
functionally different and that certain mental processes/behaviours are predominantly controlled
by one hemisphere rather than the other. The corpus callosum is a bundle of nerve fibres which
facilitates interhemispheric communication, allowing messages to be transmitted across the left
and right hemispheres. Sperry was the first to investigate hemispheric lateralisation using split-
brain patients, wherein patients had undergone a commissurotomy: the corpus callosum is
severed. This was cut to reduce epileptic seizures. The research aimed to investigate the extent
to which the two hemispheres are specialised for certain functions using different types of
experiments (‘describe what you see,’ ‘tactile test,’ ‘drawing task ’).
Sperry’s ‘describe what you see’ procedure is as follows: the participants visually fixate on a dot
in the centre of a screen, with information presented on the left or right visual fields. For
example, the words key and ring are presented on separate halves of the screen. The
participants are then asked questions and have to respond verbally or physically without seeing
what their hands are doing. When ‘key’ and ‘ring’ are presented, the participants verbally say
‘ring’ when asked to respond. When asked to respond physically, their left hand gestures at a
ring.
Sperry concluded that both hemispheres are trying to answer the question but are not able to
integrate the information due to the severed corpus callosum. Information from the right visual
field is processed by the left hemisphere, which can respond verbally as it contains the
language centre, but cannot move the right hand as it has no centre for visual spatial abilities.
Information from the left visual field is processed by the right hemisphere, which can see the
image and control the movement of the left hand towards the key, but cannot respond verbally
due to having no language centre.
There was only a sample size of 11 participants for this study as the number of people with a
severed corpus callosum due to severe epilepsy is small; hence, the generalisability of these
findings is limited. In Sperry’s research, the behaviour of split-brain participants was compared
to a neurotypical control group. However, none of the control group had epilepsy; hence, any
differences between the groups may have been due to the lack of epilepsy rather than the split-
brain procedure, which is a confounding variable. Some of the unique features of the split-brain
patients’ cognitive abilities may have been due to epilepsy. Cause and effect relationships are
difficult to establish.
Ultradian & Infradian Rhythms
Biological rhythms are cyclical patterns in biological systems. Ultradian rhythms last for a
period less than 24 hours; for example, sleep patterns. They tend to occur more than once over
24 hours. This cycle alternates between REM (rapid eye movement) and NREM (non-rapid eye
movement), and consists of five stages, starting at light sleep, progressing into deep sleep and
then into REM sleep. This cycle repeats itself about every 90 minutes–on average, a person
might experience five full cycles per night.
However, individual differences in humans may cause difficulties when studying the sleep cycle.
Tucker et al. found significant differences between participants in terms of duration of each
sleep stage, particularly stages 3 and 4 (deep sleep NREM, the stages preceding REM.) This
study was carried out in a controlled lab setting, meaning the differences in sleep patterns could
not be attributed to extraneous variables, but rather only to the biological factors/differences
between participants. Therefore, an idiographic approach should be conducted regarding
research into ultradian rhythms, rather than a nomothetic approach that generates general laws;
hence, accounting for differences between individuals.
Infradian rhythms are biological rhythms that last a period longer than 24 hours; they may be
weekly, monthly or yearly. A monthly infradian rhythm is the menstrual cycle, which is regulated
by hormones that either promote ovulation or stimulate the uterus for fertilisation. Ovulation
occurs halfway through the cycle, when oestrogen levels are highest, and usually lasts 16-32
hours. After ovulation, progesterone levels increase, ready for possible embryo implantation.
Whilst one may infer that infradian rhythms are governed by internal factors, research suggests
that the menstrual cycle is, to some extent, governed by exogenous zeitgebers. Reinberg
(1967) examined a woman who had spent three months in a cave with only a small lamp to
provide light; Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7
days. Lack of light (an exogenous zeitgeber) in the cave impacted her menstrual cycle,
therefore demonstrating the effect of external factors on infradian rhythms.
There is further evidence to suggest that exogenous zeitgebers impact infradian rhythms.
Russel et al (1980) found that menstrual cycles became synchronised 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. Despite these two groups being separate, their menstrual
cycles synchronised.
This therefore suggests that the synchronisation of menstrual cycles can be affected by
pheromones, indicating that external factors and exogenous zeitgebers should be taken into
account when investigating infradian rhythms. Perhaps a more holistic approach should be
taken, rather than a reductionist approach that considers only endogenous influences.
, Circadian Rhythms
Lasts 24 hrs. Sleep/wake cycle; light provides primary input, acting as external cues (exogenous
zeitgebers).
Siffre – stayed in a cave for 2 months. Absence of exogenous zeitgebers significantly impacted
his circadian rhythm; when surfacing, he believed the date to be a month earlier than it was.
Hemispheric Lateralisation
Hemispheric lateralisation refers to the idea that the two hemispheres of the brain are
functionally different and that certain mental processes/behaviours are predominantly controlled
by one hemisphere rather than the other. The corpus callosum is a bundle of nerve fibres which
facilitates interhemispheric communication, allowing messages to be transmitted across the left
and right hemispheres. Sperry was the first to investigate hemispheric lateralisation using split-
brain patients, wherein patients had undergone a commissurotomy: the corpus callosum is
severed. This was cut to reduce epileptic seizures. The research aimed to investigate the extent
to which the two hemispheres are specialised for certain functions using different types of
experiments (‘describe what you see,’ ‘tactile test,’ ‘drawing task ’).
Sperry’s ‘describe what you see’ procedure is as follows: the participants visually fixate on a dot
in the centre of a screen, with information presented on the left or right visual fields. For
example, the words key and ring are presented on separate halves of the screen. The
participants are then asked questions and have to respond verbally or physically without seeing
what their hands are doing. When ‘key’ and ‘ring’ are presented, the participants verbally say
‘ring’ when asked to respond. When asked to respond physically, their left hand gestures at a
ring.
Sperry concluded that both hemispheres are trying to answer the question but are not able to
integrate the information due to the severed corpus callosum. Information from the right visual
field is processed by the left hemisphere, which can respond verbally as it contains the
language centre, but cannot move the right hand as it has no centre for visual spatial abilities.
Information from the left visual field is processed by the right hemisphere, which can see the
image and control the movement of the left hand towards the key, but cannot respond verbally
due to having no language centre.
There was only a sample size of 11 participants for this study as the number of people with a
severed corpus callosum due to severe epilepsy is small; hence, the generalisability of these
findings is limited. In Sperry’s research, the behaviour of split-brain participants was compared
to a neurotypical control group. However, none of the control group had epilepsy; hence, any
differences between the groups may have been due to the lack of epilepsy rather than the split-
brain procedure, which is a confounding variable. Some of the unique features of the split-brain
patients’ cognitive abilities may have been due to epilepsy. Cause and effect relationships are
difficult to establish.
