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ESSAY Discuss research into ultradian rhythms
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Betsy EdwardsDiscuss research into ultradian rhythms. (16 marks)
An ultradian rhythm is a biological rhythm that lasts less than 24 hours, for example the sleep
cycle (investigated by Dement and Kleitman). This is a 90 minute cycle of four non-rapid eye movement
(NREM) stages and one rapid eye movement (REM) stage. The cycle is repeated throughout the course
of the night. EEG scans show that the first two stages of NREM – characterised by alpha and theta waves
– are light sleep that is easily woken from. Muscle activity, breathing and blood flow are all reduced, and
heartbeat becomes irregular. Stages three and four of NREM – characterised by delta waves – are much
deeper sleep that is difficult to wake from; an individual may experience sleep inertia if woken at this
stage. In the REM stage, our body is paralysed yet eye movement is fast and brain activity resembles
awake brain activity. Heart rate and breathing also increase. Research shows that the repeating cycle of
stages is 1, 2, 3, 4, 3, 2, REM.
A strength of research into the sleep cycle is that it has increased our understanding of
dreaming. Dement and Kleitman found that 90% of participants who were awoken in the REM stage
could recall their dream, compared to 7% of participants awoken in a NREM stage. Furthermore, there
was a strong correlation between brain activity and how vivid the dreams were. This evidence is useful
because it has been used to increase our understanding of memory; for example, from this research
Dement proposed the theory of dynamic stabilisation, which suggests the firing of neurones in REM –
associated with dreaming – is essential for memory consolidation.
Our knowledge of ultradian rhythms has had practical applications for workers and students.
Kleitman suggested that a cycle similar to the sleep cycle occurs throughout waking hours; we
experience a 90 minute basic rest activity cycle (BRAC), consisting of alternating periods of alertness and
fatigue. Ericsson’s research demonstrates this, as he found the best violinists have three practice
sessions each day, each lasting no more than 90 minutes, with breaks in between each session. Our
knowledge of BRAC helps to increase worker productivity and student learning by encouraging frequent
breaks to maximise periods of alertness. However, the fact that many professions and learning
institutions impose much longer working periods between breaks suggests that our rhythms are not
fixed and can be overridden; this may imply that social cues act as exogenous zeitgebers that influence
ultradian rhythms, weakening our understanding as it appears to be incomplete.
Our knowledge of ultradian rhythms appears to be limited as we cannot explain individual
differences. For example, some individuals can easily nap during the day, whereas others cannot. In
addition, Tucker found large differences in sleep patterns and responses to 36-hour sleep deprivation.
This may suggest that there is another factor – such as a genetic predisposition – influencing our sleep
cycles, meaning that our current knowledge is incomplete.
Word count: 163 + 316
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