Activation-Synthesis Theory - Hobson and McCarley (1977)

The Activation-Synthesis theory is the biological theory of dreaming, which is very different from Freud's psychological theory.

The Activation-Synthesis theory suggests that dreams are random messages in the brain being interpreted to make a story. Messages are activated randomly, then synthesised (put together) into a story.

Hobson and McCarley from their biological viewpoint said that there is a dream state generator in the brain and this part of the brain that gives a dream state is switched on during REM sleep.

Research has shown that sleep goes through about five cycles of four stages each, and after each cycle of four stages, there is REM sleep.

REM sleep is when there is Rapid Eye Movement (when the eyelids can be seen flickering very quickly). This happens around five or more times a night. As dreaming during REM sleep is easily recognisable, scientists can measure electrical brain activity in the brain during REM sleep using an EEG (electroencephalograph).

During REM sleep, any incoming information from the senses (sight, sound, touch, taste, smell) is blocked. This is known as Sensory Blockade (no information enters through the senses).

Physical movements are also blocked in REM sleep. This is known as Movement Inhibition (the body is paralysed and there is no movement). So during REM no information is coming into the brain and no outgoing movements are being made by the body.

However, during REM sleep, the neurons in the brain are activated because there are random impulses that 'give' information as if it were from the senses. This is known as Random Activation (neurons are active randomly, not deliberately) and is the 'activation' part of the activation-synthesis theory.

The information that comes from inside the brain itself is known as internally-generated information. The brain then tries to make sense of the 'nonsense' it has generated. It is synthesising the information to make it into a story, and this is the 'synthesis' part of the theory.

Evidence that Hobson and McCarley gave for their explanation of dreaming is that REM sleep happens regularly throughout a night's sleep and happens regularly night after night. 

Sleep labs study sleeping and everyone observed…