There's new evidence that schizophrenia could be related to our immune system – a discovery which could radically change the way the condition is treated.

Photo: MRC London Institute of Medical Sciences

No one really knows what causes schizophrenia, the mental disorder that distorts a person's behaviour, ideas and moods. It's a condition that affects 1 percent of the population here in New Zealand.

Symptoms include delusional thinking, paranoia, hearing voices and a lack of motivation, and the prevailing theory is that it's caused by too much dopamine in the brain.

Dopamine is a chemical messenger that's released when something unexpected happens: it's a chemical alert to pay attention, get ready to respond, and then learn from the experience. This experience then helps you model the world around you and function in it. It's the ability to update these models that lets us get on in life, especially in the social world.

So if the dopamine signal isn't working properly and it becomes overactive, the brain is constantly on high alert and ready to respond when there's nothing going on. This can lead to delusions and a detachment from reality, as the brain tries to work out what's happening.

This explains some of the symptoms, but it doesn't explain others like difficulties with planning, memory and motivation, and new research suggests that our Immune system could be a factor.

Microglia, which are immune cells, wash around the brain and act like cleaners, taking away wasted and unused neural connections and protecting the brain from infection. In schizophrenia, especially in the early stages, there's a surge in the number and the activity of these cells.

The thinking is that this leads to an 'over pruning' of connections between neurons, damaging links that are needed for the brain to function properly.

Photo: Supplied

Oliver Howes is a professor of molecular psychiatry at the Medical Research Council - London Institute of Medical Sciences and he and his team have been researching the link between the immune system and schizophrenia.

"This is one of the most exciting things I think that's happening in brain science in the last few years, the realisation that microglia aren't just there to defend against infection or deal with damaged and decaying cells but actually play this really key, fundamental role in pruning away the connections that we don't need." Professor Oliver Howes