Biological Rhythms, Sleep, and Dreaming

A cyclical variation over some period of time in physiological or psychological processes (Gross and McLlveen, 2000)

Circadian rhythms occur once every 24 hours. For example, the human sleep/waking cycle and also physiological systems such as the control of body temperature. Circadian rhythms are important as they synchronise behaviour and body states to changes in the environment.

Infradian rhythms have a cycle longer than 24 hours. For example the human menstrual cycle. Included in infradian rhythms are circannual rhythms which are yearly rhythms.

Ultradian rhythms have more than one complete cycle every day. An example of this is sleep which consists of a 5 stage cycle which is repeated roughly every 90 minutes, multiple times throughout a single period of sleep.

Stage 1

Stage 1 is the beginning of the sleep cycle, and is a relatively light stage of sleep. Stage 1 can be considered a transition period between wakefulness and sleep. In Stage 1, the brain produces high amplitude theta waves, which are very slow brain waves. This period of sleep lasts only a brief time (around 5-10 minutes), and if you awaken someone in the stage, they might report that they weren't really asleep.

Stage 2

Stage 2 is the second stage of sleep and lasts for approximately 20 minutes. The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Body temperature starts to decrease and heart rate begins to slow.

Stage 3

Deep, slow brain waves known as delta waves begin to emerge during stage 3 sleep. Stage 3 is a transitional period between light sleep and a very deep sleep.

Stage 4

Stage 4 is sometimes referred to as delta sleep because of the slow brain waves known as delta waves that occur during this time. Stage 4 is a deep sleep that lasts for approximately 30 minutes. Bed-wetting and sleepwalking usually occur at the end of stage 4 sleep.

Stage 5

Most dreaming occurs during the fifth stage of sleep, known as rapid eye movement (REM) sleep. REM sleep is characterized by eye movement, increased respiration rate, increased brain activity. REM sleep is also referred to as paradoxical sleep because while the brain and other body systems become more active muscles become more relaxed. Dreaming occurs due because of increased brain activity, but voluntary muscles become paralyzed.

Electroencephalogram (EEG)

• Measures brain activity
• Uses electrodes attached to the scalp
• Allows researchers to determine whether people are awake or asleep, and in which stage of sleep they are in.

Electromyogram (EMG)

• Measures muscle activity
• Whether relaxed or contracted

Electrooculogram (EOG)

• Measures eye movement
• Why?- dreaming is usually accompanied by REM (rapid eye movement)