Biological Rhythms - Ultradian

What is an ultradian rhythm?

A biological process that repeats more frequently than once every 24 hours (eg minutes/hours)

Electroencephalogram brainwave features: Frequency

How close the waves are to each other (waves per second in Hz)

Electroencephalogram brainwave features: Amplitude

The size of the brain wave (change in voltage)

What are the 5 distinctive features of electroencephalogram brainwaves?

• Delta

• Theta

• Alpha

• Beta

• Gamma

*Theta and Delta distinguish sleep stages

What are the 4 stages of the sleep cycle?

1. Light sleep

2. Deeper sleep

3. Deepest sleep

4. REM (Rapid Eye Movement Sleep)

Stage 1 → Light sleep

‘Feeling asleep’ sensation. Easy to wake and the body may move suddenly (hypnic jerks). There may be a sensation of falling, mild auditory or visual hallucinations (hypnagogic hallucinations). EEG shows theta waves, slow frequency but high amplitude in comparison to awake.

Stage 2 → Deeper sleep

Deeper than stage 1. Harder to wake, the body is relaxed, heart rate and body temperature are lowered, and the eyes are still. EEG shows slow theta, but occasional activity called sleep spindles and K complexes

Stage 3 → Deepest sleep

Very difficult to wake, body at its most relaxed with heart rate at its lowest. Identified on the EEG by the presence of slow frequently and large amplitude delta waves (slow wave sleep)

Stage 4 → REM (Rapid Eye Movement Sleep)

Brain returns to active state passing back through Stage 2 and Stage 1, REM is similar to wakefulness as seen on EEG however the body is paralysed. Characterised by rapid eye movement, and associated with dreaming, as when woken people will report vivid dreams in this stage

How does the sleep cycle go?

The brain returns to stage 1 after REM, repeating the cycle up to 5 times in one night. Each cycle tends to include a larger proportion of REM sleep and shorter duration of stage 3

AO3 - Dermot and Kleitman (1957)

Stage 1: EEG recordings made of 33 participants over a nights sleep. Brain waves followed a cyclic pattern of activation, with bodily relaxation occurring during slow wave sleep and rapid eye movement during periods of high activation. Stage 2: 9 participants woken at different stages in their sleep cycle reported dreaming more frequently when woken in the REM stage

AO3 - Shapiro (1981)

Ultramarathon runners showed longer sleep after intense physical activity. Also an increased proportion in slow wave sleep, suggesting slow wave sleep (stage 3) is for physical recovery of the body. EEG of 10 patients recovering from drug overdose showed increased REM sleep, suggesting REM is for mental recovery

AO3 - Individual differences

The overall pattern of sleep stages is consistent however there are some individual differences with newborn babies spending 80% of sleep in REM compared to 20-25% in adults. Suggesting the stages of sleep are not a simple process but adapt to the developmental needs of the individual

AO3 - Technology and sleep

Technology and devices based on understanding sleep stages have been developed. These track sleep and help individuals improve sleep. Avoiding waking in stage 4 stops people feeling groggy and disoriented. This technology leads to a happier, healthier and more economically productive population

AO3 - Czeisler (1980)

Circadian and ultradian rhythms seem to be connected and perhaps shouldn’t be seen as separate processes, Czeisler showed the longest period of REM sleep coincides with the lowest point in the circadian body temperature cycle. This could mean both processes could use the same internal body clock also known as the endogenous pacemaker (SCN)

AO3 - Understanding encourages new research

The development of more sophisticated EEG’s and other techniques is improving our understanding of the sleep cycle, leading in 2007 to combining old stages 3 and 4 into the new stage 3