outline and evaluate ultradian rhythms Flashcards
outline
Ultradian rhythms are rhythms that occur more than once in a 24-hour period.
Psychologists have identified 5 distinct stages of sleep that last a total of 90 minutes per cycle, which continues throughout the course of the night.
Each of these stages is characterised by differences in levels of brain wave activity (which can be monitored using an EEG).
All biological rhythms are controlled by 2 factors: endogenous pacemakers (the body’s internal biological clock) and exogenous pacemakers (external changes in the environment).
Stages 1 and 2 consists of light sleep where a person is easily woken, characterised by slow and rhythmic brain activity.
Stages 3 and 4 is a deep sleep where a person is difficult to wake, characterised by even slower and a greater amplitude of brain waves.
Stage 5 is where the body is paralysed yet brain activity resembles an awake brain, referred to as rapid eye movement (REM) sleep as there is fast activity from the eyes under the eyelids - highly correlated with the experience of dreaming.
outline study
Hobson investigated two groups of cells – REM-On and REM-Off which he found appear to control the activity of the other.
Hobson found that when REM-Off cells are active, they inhibit (reduce) the activity of REM-On cells.
So, as a person falls asleep, the REM-Off cells become less and less active.
This in turn increases the activity of REM-On cells and so we enter the REM sleep.
After a period, this effect is quickly reversed and so we leave REM sleep entering NREM sleep once again.
This pattern then repeats itself during sleep giving us the sleep stages.
This suggests that stages of sleep are controlled by endogenous pacemakers which help to regulate the cycle.
limit
A limitation of research into ultradian rhythms is that there are high individual differences, which is when there is variability between individuals which have not been controlled for.
For example, Tucker found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep).
This demonstrates there may be genetic individual differences in ultradian rhythms.
Future research should therefore focus on these differences during investigations into sleep cycles.
strength
A strength of Ultradian rhythms is that there is strong supporting evidence. Dement and Kleitmen (1957), found that brain wave activity varied between different stages of sleep.
They identified that during REM sleep and dreaming, brain activity was at its highest, and participants woken during this time had very accurate recall of their dreams.
This suggests that different stages of sleep are governed by biological processes including brain wave activity.
