Ultradian rhythms are biological rhythms that occur more than once a day, with a period shorter than 24 hours.eg. stages of the sleep cycle and meal times.
In the stages of the sleep cycle, one cycle is roughly 90mins and the stages are characterised by different levels of brain wave activity which can be monitored with the use of an EEG.
Stage 1 and 2 - Light sleep where a person can be easily woken. brain waves at high frequency and low amplitude. alpha waves continue in stage 2 and sleep spindles. Person can be easily woken - known as hypnic jerks. feelings of sudden falling and hallucinations may also be present.
Stage 3 n 4 - Deep sleep/slow wave sleep. Delta waves in the brain - with lower frequency and higher amplitude. it is difficult to wake someone.
Stage 5 - Body is paralysed but brain is awake. Theta waves produce rapid eye movement (REM) where dreams are seen but can also occur at deep sleep. (desynchronised brain waves).
