Ultradian rhythms are biological rhythms that occur more than once every 24 hours. The stages of sleep are a well researched example. They are controlled endogenously and are measured on an electroencephalograph (EEG). In stage one, theta waves of low amplitude and high frequency can be observed. Heart rate, breathing and temperature (HR, B&T) begin to drop. In stage two sleep spindles and k-complexes (mental responses to external stimuli) are seen.
Stage three is the first stage of slow wave sleep (SWS). Here, delta waves of high amplitude and low frequency can be observed. In stage four, delta waves make up around 50% of waves and HR, B&T are at their lowest. After stage four, the sleeper ascends the ‘sleep staircase’, but instead of entering stage one they enter Rapid Eye Movement (REM) or ‘paradoxical’ sleep. HR B&T are almost as high as waking levels, the waves are theta waves and most dreaming occurs. We go through this cycle approximately 8 times in 5 hours (i.e. every 90 minutes) and there is evidence that this endogenously controlled ultradian rhythm can be influenced by external zeitgebers.
One strength of most explanations of ultradian rhythms is that they suggest an interaction between biology (endogenous pacemakers) and the environment (exogenous pacemakers). For example, they acknowledge that stage two sleep is influenced by the environment in the form of k-complexes (mental responses to external stimuli). This is positive as most psychologists a combination of external and internal factors is sensible. The explanations can therefore be praised for taking a more holistic approach.
One issue with many explanations of ultradian rhythms is that they are nomothetic. This means they assume that everyone experiences sleep in the same way. For example, in Southern Europe and South America people take ‘siestas’ in the afternoon, so their sleep pattern may be different due to altered sleeping hours. Therefore a more idographic approach (focused on the individual) would be more suitable so by taking a nomothetic approach explanations may be too simplistic.
Evidence supporting the idea that exogenous zeitgebers can affect the endogenously controlled ultradian rhythm of sleep stages comes from Dement and Wolpert. In a sleep laboratory, they sprayed REM sleepers in the face with water. They found that those sprayed reported dreaming of water more frequently than those who were not sprayed. This is positive because it seems water (an exogenous zeitgebers) can influence the ultradian rhythm of sleep stages.
One problem with this research is that it was conducted in the artificial setting of a laboratory. This means that the setting did not reflect the participants’ natural environment. For example, sleeping in a laboratory may have caused the participants to have more disturbed sleep. This is a problem as this may have caused the results to be misleading, meaning the results may have lacked internal validity.