Dreaming as a by-product of the sleeping brain

1. Hobson and McCarley put forward a biological explanation of dreaming in 1977.
2. A psychological explanation starts with meaning and asks what a dream is about, but this one starts with electrical activity and asks where a dream comes from.
3. The name has two halves: activation is the firing, and synthesis is the brain making sense of it.

Random activation

1. During REM sleep, bursts of signals fire from the pons, low down in the brainstem.
2. These bursts are random, meaning they carry no message and are not aimed at anything in particular.
3. They travel up to the higher parts of the brain, which treat them as though they were real incoming information.

Sensory blockade

1. At the same time, signals coming in from your eyes, ears and skin are blocked from reaching the sleeping brain.
2. The only activity available to work with is therefore the activity the brain is generating itself.
3. That is why a dream can feel completely real while you are in it, because nothing is arriving from outside to contradict it.

Movement inhibition

1. Signals travelling out to your muscles are blocked as well, so your body stays still.
2. You do not act the dream out, however much running or fighting is going on inside it.
3. This is protective, since a sleeper who carried out everything they dreamt would soon be hurt.

Synthesis and where the dream comes from

1. The cerebral cortex, the thinking part of the brain, is left holding a stream of activity with no source it can identify.
2. Making sense of whatever it receives is what the cortex does all day, and it carries on doing it at night.
3. It pulls the random bursts together into the nearest story it can build out of memories and familiar images.
4. That story is the dream you wake up with, so on this account the dream is the brain's explanation rather than a message it was sent.

Weighing the theory up

1. Strength: it rests on brain activity that can be recorded and measured, so it is far more objective than interpreting what someone says about a dream.
2. Strength: it explains bizarreness cheaply, because a story assembled from random material is bound to jump about.
3. Weakness: it is reductionist, cutting a vivid personal experience down to random firing and a tidying-up process.
4. Weakness: it struggles with dreams that recur, because genuinely random starting signals should not produce the same dream night after night.

Turning this into marks

1. Name Hobson and McCarley and take random activation, sensory blockade and movement inhibition in order.
2. Say the signals come from the pons during REM and carry no meaning of their own.
3. The mark most often lost is describing the mechanism without ever weighing the theory.