Psychiatric Imaging finds clue to psychosis
Delight is the brain’s way of telling us that something new that we are experiencing is good. Some seek out this feeling compulsively: the Indian philosophical school of Cãrvãka taught 2500 years ago that pleasure was the ultimate goal in life. But as we all know, not every repeat experience conjures that same delight the 100th time as it did the first. Things lose their shine: the bright sparkling wonder of the World we experience as children becomes dull over the years, and it is hard to live our lives with the same constantly positive outlook as Cãrvãka proposed.
The signalling molecule that helps our brains categorise an experience as being good – and worth repeating – is called dopamine. This molecule makes us feel great. As well as having a positive impact by making food taste good and sex fun, dopamine plays a role in addiction, because of the compulsion to repeat experiences. Crucially, it also plays an important part in the development of psychosis – including illnesses such as schizophrenia and bipolar disorder, which affect 1 in every 100 people. For these people every minute event takes on higher significance, meaning their brains are overloaded, because of increased dopamine levels. “For people with schizophrenia, dopamine levels are high, and this is thought this to mean irrelevant stimuli come to assume greater importance,” explained CSC Group Head Dr Oliver Howes to a group of design Master’s students at Central Saint Martins last year; they were learning about the physiological bases of disease.
What hasn’t been clear before is what the causal relationship between increased dopamine and increased risk of psychosis. Did those unfortunate enough to develop psychosis subsequently have an increased capacity to make dopamine, or was it the other way round? Dr Howes’ new findings, reported in the July 2011 issue of the American Journal of Psychiatry, show that patients deemed at high risk of developing psychosis – those who had experienced symptoms that typically lead on to psychosis such as mild changes in behaviour or inability to deal with stress – already had an increased capacity to make dopamine. This is the first piece of evidence that increased dopamine levels may lead to psychosis rather than the other way round. And this change in dopamine seems to be a key indicator as to whether individuals who seem to be at risk really do go on to develop psychotic illnesses.
“Our finding that there was no change in the dopamine function in patients who presented with psychiatric problems but got better suggests that the elevated dopamine function is specific to the later development of psychosis. We are looking to see if the scan can be used to as a predictive test,” says Dr Howes. “The holy grail is to find a way of preventing these devastating illnesses before they start. Our finding that dopamine function is elevated in people who go on to develop psychotic illnesses is an important clue as to what causes them.”
He continues: “Future treatments could target this part of the brain’s dopamine system to prevent the full development of the illness. As roughly 1 in 10 people with schizophrenia die from suicide, predominantly in the first few years after the illness starts, a treatment that prevents the full illness could save many lives as well as alleviating suffering.”
SJ
Reference:
Howes, O. D., Bose, S. K., Turkheimer, F., Valli, I., Egerton, A., Valmaggia, L. R., Murray, R. M., McGuire, P., Jul. 2011. Dopamine synthesis capacity before onset of psychosis: A prospective [18F]-DOPA PET imaging study. The American journal of psychiatry.
http://dx.doi.org/10.1176/appi.ajp.2011.11010160
