How often does a school friend/work colleague come up to in the morning and say, "Oh my god, I had the WEIRDEST dream last night. . . ."? You might them tune out as they go into the details of some totally illogical dream that somehow involved you and dogs playing poker.

Hobson and McCarley's activation-synthesis theory was developed to explain why we dream, and in particular why they so often make little logical sense. Most of you would be familiar with Freud's wish fulfilment theory, which proposed that what is expressed in our dreams are the wishes, desires or fantasies that we are unable to fulfil in our waking lives, often because we could experience too much anxiety or guilt. To protect ourselves from the anxiety associated with the content of the dream, Freud suggested that we often disguise the real issue by dreaming in symbols.

In 1977, Alan Hobson and Robert McCarley published research which argued that dreams were random, meaningless activities carried out by the nerve cells in the sleeping brain. From experiments performed on cats, Hobson and McCarley identified structures of the brain which appear to be directly associated with REM sleep - the pons and reticular activating system in the brain stem. These structures appear to be involved in shutting down the brain's access to movement during REM sleep, resulting in the 'muscular paralysis' we experience during this stage. When we are awake, particular nerve cells in the brain stem are activated enabling us to run, walk etc. When we are in REM sleep and our body is in a state of 'paralysis', certain neurons in the brain are randomly activated. Therefore the neural messages about body movement cannot be acted upon. Higher brain centres detect this neural activity and the information is assembled in an attempt to give some sort of meaning to these random and uncoordinated messages by synthesising them or combining them with existing knowledge and memories. According to Hobson and McCarley the result is a dream. For example, if neurons fire in the part of the brain which controls balance you might dream about falling. This is the brain's way of giving some sort of meaning to the activation of that part of the brain. According to Hobson and McCarley, the random and uncoordinated nature of the neural messages may explain why dreams are so often a disjointed connection of seemingly unrelated events.

So next time your friend/colleague recalls some boring nonsensical dream, and then asks "What do you think it all means?" tell them this equally boring, long-winded theory, and give them a taste of their own medicine!

. .. .as an after thought, apparently few years later Alan Hobson changed his mind and reported that it seems that dreams have important personal significance to the dreamer. Geeze, make up your mind!

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