Ultradian + infradian rhythms

What are ultradian rhythms?

Rhythms that span a period of less than one day.

Eg BRAC cycle

What are infradian rhythms?

Rhythms spanning more than one day.

Eg women’s menstrual cycle.

Ultradian rhythms: where do ultradian rhythms occur during sleep-wake cycles?

The five stages that make up a typical nights sleep.

What pattern does the ultradian rhythm found in human sleep follow?

A pattern of alternating REM (rapid eye movement) and NREM (non-rapid eye movement) sleep.

This consists of stages 1 to 4.

How often does the cycle repeat itself throughout the night?

Every 90-100 minutes throughout the night, with different stages having different durations.

What does a complete cycle consist of?

A progression through the four stages of NREM sleep before entering a final stage of REM sleep.

After this, the whole cycle starts all over again.

How are these different sleep stages differentiated?

Each stage shows a distinct EEG pattern.

Diagram of the characteristics of the different sleep stages

Description of what generally happens across the cycle.

As the person enters deep sleep, their brainwaves slow and their breathing and heart rate decreases.

During the fifth stage (REM sleep), the EEG pattern resembles that of an awake person - it is in this stage that most dreaming occurs.

What does Kleitman’s BRAC stand for?

Basic Rest Activty Cycle

This is a 90 minute cycle found during sleep.

Kleitmen also suggested that this 90 minute ultradian rhythm continues during the day when we aware awake.

What’s the difference between these ultradian rhythms in the night vs in the day?

During the day, we move progressively from a state of alertness into a state of physiological fatigue approximately every 90 minutes.

In the night we move through sleep stages.