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What can you learn about mental illness from brain imaging?

A PET scan of a person who uses cannabis. The red areas show the highest levels of dopamine.

A PET scan of a person who uses cannabis. The red areas show the highest levels of dopamine.

Can you learn anything about schizophrenia from scanning brains? Yes, says Michael Bloomfield, a researcher at the MRC Clinical Sciences Centre — it’s all about looking at the detail. Here he explains his work to mark Schizophrenia Awareness Week (11-17 November).

The first major revolution in the care of mentally ill patients occurred in the late 18th century. Philippe Pinel, working at the Salpêtrière Asylum in Paris, ordered the removal of chains from his patients, heralding the beginning of more psychological and humane treatments.

The second revolution came 100 years later when psychotherapy was first used, followed by a third in the mid-20th century with the discovery of psychiatric medicines.

We are now living in the midst of a fourth revolution: using modern brain imaging techniques to learn more about disease and develop new treatments.

Our brains have more than 100 billion brain cells, all of which have many connections with other cells. In fact it’s often said that there are more connections in your brain than there are stars in our galaxy. The cells ‘talk’ to each other by sending chemical signals called neurotransmitters. A neurotransmitter released from one cell acts like a key, so that when it hits a protein on the receiving cell called a receptor, this receptor is unlocked, and the message passed on.

My research uses brain imaging to study these neurotransmitters in mental illnesses such as schizophrenia. Schizophrenia is a potentially devastating illness where people have bouts of distressing symptoms including feeling frightened and hearing upsetting voices.

All of us have a neurotransmitter called dopamine. Since drugs used to treat people with schizophrenia all work by blocking dopamine, the theory went that people with schizophrenia have high levels of dopamine in their brains.

My team, led by Oliver Howes at the MRC Clinical Sciences Centre, has used a brain scanning technique called Positron Emission Tomography to show that people with schizophrenia do indeed tend to have high dopamine levels in their brains, and that the higher the dopamine levels, the more severe their symptoms.

Positron Emission Tomography (PET for short) uses something called a radiotracer which acts a bit like a dye. There are a variety of dyes available which can attach to different chemicals in the body. The dyes give off a small amount of radiation which is then detected by the scanner and, in our case, allows us to measure small changes in neurotransmitters in the living brain. This means we can measure the effect that different medicines have on neurotransmitters.

We also found that there is a group of people with schizophrenia who don’t seem to be producing high levels of dopamine. These people don’t tend to get better with the standard dopamine-blocking medicines either, so we need to work out which neurotransmitters are implicated in this group of people so that better drugs can be developed to help them.

Our most recent research found that cannabis use, which increases the risk of schizophrenia, is also associated with lowered dopamine production. This might explain how cannabis can be addictive and why some cannabis users lack motivation. We know that dopamine is an important neurotransmitter in our brain’s motivation system and other drugs that people can become addicted to, like cocaine, are associated with “blunted” dopamine levels.

It’s my hope that understanding what is happening chemically within the brains of people with mental illnesses will mean that tomorrow’s patients will have treatments that work better, faster and lead to fewer side-effects.

Michael Bloomfield

Schizophrenia Awareness Week runs from 11-17 November 2013.

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