Age-Related Macular Degeneration

When visual signals leave the eye they go to the back of the brain (the occipital lobe) to the primary visual receiving area, called V1.

From V1 the signals are relayed to a series of areas, each specialised in a different aspect of seeing. There is an area for movement, an area for colour, several for faces, one for landscapes and many others.

Scanning studies have revealed what happens in the brains of people while they hallucinate.

What happens in the brain?

With our eyes open, the visual brain expects to receive and process a flood of complex electrical signals. In people with eye disease or a break in the visual pathways, what was once a flood becomes a trickle. This leaves the visual areas of the brain with little to do.

The idle visual brain cells, waiting for an appropriate trigger, begin to fire spontaneously. If this happens in the colour area, people experience hallucinations of colour; if in the object area, they see objects and so on.

After a while, the visual brain gets used to the lower level of information from the eye and the spontaneous firing lessens or stops. This explains why, for many people, the hallucinations gradually reduce over time.