Australian researchers say they have identified the neural mechanism that could trigger hallucinations. The discovery could lead to more effective drugs for treatment of schizophrenia. The mechanism in questions hinders reward identification and decision-making.
The study led by Dr Thomas Weickert, of UNSW's School of Psychiatry, and published in the journal Molecular Psychiatry
, found that an area deep in the brain called the ventral striatum, which usually lights up with activity in response to rewards in healthy adults, was relatively unresponsive in people suffering from schizophrenia.
Specifically, the study showed that people with schizophrenia were unable to distinguish between expected and unexpected rewards, frustrating their efforts to deal with unpredictability in daily life and making it difficult for them to make decisions in their own best interests.
Reward responses are important in many areas of learning because they help us to redirect attention and behaviour towards things that are beneficial to us, Dr Weickert said. The ventral striatum is connected to other parts of the brain that are important in decision making, planning and cognition and is, consequently, attracting increasing interest from researchers.
Dr Weickert said healthy adults in the study had no trouble dealing with unpredictability, whereas people suffering from schizophrenia were not able to tell the difference between expected and unexpected rewards.
"Using functional MRI images we could see that this region of the brain wasn't firing correctly. People with schizophrenia often have difficultly determining what is beneficial for them and what is not, so they have trouble taking cues from their environment and, consequently, can make some bad decisions," Dr Weickert said.
"This work may help us understand the neurological underpinnings of symptoms such as hallucinations and delusions since we found a relationship between brain activity in this reward region and psychotic symptom severity."
"As the people we studied were on medication we found that current drug treatments for schizophrenia are not helping this part of the brain function any better. Ultimately, we would like to see some new medications that will improve ventral striatum function," Dr Weickert said.
"These results should help direct further studies on the ventral striatum in which we can look at the effect of therapies and, potentially, genetic influences on this particular region of the brain."
Researchers believe the onset of schizophrenia is triggered by a complex interaction between genetic susceptibilities and environmental factors. It is a lifelong, chronic disease currently without a cure. One in 100 young people will develop schizophrenia, and many will be permanently disabled; at a cost of about $2 billion a year in Australia in direct medical bills and loss of productivity.