Activation-synthesis theory (Hobson and McCarley 1977)

Activation-synthesis theory (Hobson and McCarley 1977)

Unlike other research about sleep and dreaming, Hobson and McCarley’s theory focuses specifically on the neurobiological aspects of this, in order to try and explain why and how people dream. This can be quite a difficult concept to understand so make sure you read through each part thoroughly.

Activation synthesis

 Hobson and McCarley argue that dreams occur when the mind tries to make sense of the activity in the brain which is taking place whilst someone sleeps. They also believe that the brain activity that occurs (especially during REM sleep) serves some other purpose, such as restoration and protein synthesis.

The researchers point out that brain activity is present during REM sleep but all muscles are paralysed causing movement inhibition. As well as this, REM sleep means that the brain is not picking up sensory information, which they refer to as sensory blockade. Despite this, they argue that random messages are being sent in the brain and this is the ‘activation’ part of their theory.

These random thoughts are understood to come from neurons in the brain, which are activated and then fired – meaning that an electrical impulse occurs, causing neurochemicals to be released. As we saw in an earlier unit, this means that the neurochemicals will cross a synaptic gap and messages (which are ‘thoughts’ in this case) are sent.

Hobson and McCarley believe that these random thoughts are actually the basis of dreaming as several things come together (or are synthesised) in order to make this happen. The random thoughts, which are triggered by firing neurons, generate internal information. The brain then automatically tries to make sense of this information and this is when a person begins to dream, just as it would try to make sense of information in an environment when the person was awake.

Strengths of the activation-synthesis theory

  • The evidence presented by Hobson and McCarley is compelling; when people sleep in a laboratory and are observed, REM sleep does appear to be a time when dreaming would occur as muscles and senses are not functioning and therefore the brain has to make sense of random information
  • The theory has provided a basis for further investigation of the theory, which is ongoing even today.

Weaknesses of the activation-synthesis theory

  • Other work in this area has been carried out on animals, which cannot be applied to human behaviour
  • Some dreams appear to have specific meaning to the individual, which counteracts the idea that the thoughts that dreams are based on are completely random.
The activation-synthesis theory
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