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Summary biopsychology - biological rhythms
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biopsychology notes on biological rhythms
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Biological rhythms:Circadian rhythm – 24 hours, reset by levels of light
The sleep-wake cycle is an example of a circadian rhythm, which dictates when humans and animals
should be asleep and awake
Light provides the primary input to this system, acting as the external cue for sleeping or waking,
which when detected by the eye, 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 wakefulness are not determined by the circadian rhythm alone, but also
by homoeostasis
When an individual has been awake for a long time, homeostasis tells the body that there is a need for
sleep because of energy consumption
This homeostatic drive for sleep increases throughout the day, reaching its maximum in the late
evening, when most people fall asleep.
Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of
the morning (36oC at 4:30 am) and at its highest in the early evening (38oC at 6 pm). Sleep typically occurs
when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep
cycle promoting feelings of alertness first thing in the morning.
Studies:
Siffre (1975) - found that the absence of external cues significantly altered his circadian rhythm:
When he returned from an underground stay with no clocks or light, he believed the date to be a
month earlier than it was. This suggests that his 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 his thinking that
fewer days had passed.
Duffy et al. (2001) - found that ‘morning people’ prefer to rise and go to bed early (about 6 am and
10 pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am). This
demonstrates that there may be innate individual differences in circadian rhythms, which suggests
that researchers should focus on these differences during investigations.
Ultradian rhythms - last fewer than 24 hours and can be found in the pattern of human sleep. This cycle
alternates between REM (rapid eye movement) and NREM (non-rapid movement) sleep and consists of five
stages. The cycle starts at light sleep, progressing to deep sleep and then REM sleep, where brain waves speed
up and dreaming occurs. This repeats itself about every 90 minutes throughout the night.
A complete sleep cycle goes through the four stages of NREM sleep before entering REM (Stage 5) and then
repeating. Research using EEG has highlighted distinct brain waves patterns during the different stages of
sleep:
Stages 1 and 2 are ‘light sleep’ stages. During these stages brainwave patterns become slower
and more rhythmic, starting with alpha waves progress to thetawaves.
Stages 3 and 4 are ‘deep sleep’ or slow wave sleep stages, where it is difficult to wake someone
up. This stage is associated with slower delta waves.
Finally, Stage 5 is REM (or dream) sleep. Here is the body is paralysed (to stop the person acting
out their dream) and brain activity resembles that of an awake person.
On average, the entire cycle repeats every 90 minutes, and a person can experience up to five full cycles in a
night.
Studies:
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. However, the study was carried out in a controlled
lab setting, which meant that the differences in the sleep patterns could not be attributed to
situational factors, but only to biological differences between participants. When investigating sleep
patterns, participants must be subjected to a specific level of control and be attached to monitors that
measure such rhythms. This may be invasive for the participant, leading them to sleep in a way that
does not represent their ordinary sleep cycle. This makes investigating ultradian rhythms, such as the
sleep cycle, extremely difficult as their lack of ecological validity could lead to false conclusions
being drawn
Randy Gardener – a case study, remained awake for 264 hours. While he experienced numerous
problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep
loss. After this experience, Randy slept for just 15 hours and over several nights he recovered only
25% of his lost sleep. Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very
little of the other stages. These results highlight the large degree of flexibility in terms of the different
stages within the sleep cycle and the variable nature of this ultradian rhythm.
Infradian rhythms - last longer than 24 hours and can be weekly, monthly, or annually.
A monthly 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, and usually lasts for 16-32 hours. After
the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an
embryo in the uterus.
It is also important to note that although the usual menstrual cycle is around 28 days, there is considerable
variation, with some women experiencing a short cycle of 23 days and others experiencing longer cycles of
up to 36 days.
Studies:
Russell et al. (1980) - found that female menstrual cycles became synchronised with other females
through odour exposure. In one study, sweat samples from one group of women were rubbed onto the
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