Schizophrenia linked to key ”default mode” brain system

January 22nd, 2009 - 1:41 pm ICT by ANI  

Washington, Jan 22 (ANI): Overactivation of a brain system that is involved in self-reflection in patients with schizophrenia may blur the boundary between internal and external realities and thus lead to an exaggerated focus on self, according to a new study.
It was believed that the disturbed thoughts, perceptions and emotions characterised by the disease are due to disconnections among the brain regions that control these different functions.
However, in the new study researchers found that schizophrenia also involves an excess of connectivity between the so-called default brain regions.
These default regions are involved in self-reflection and become active when we are thinking about nothing in particular, or thinking about ourselves. “People normally suppress this default system when they perform challenging tasks, but we found that patients with schizophrenia don”t do this. We think this could help to explain the cognitive and psychological symptoms of schizophrenia,” said John D. Gabrieli, a professor in the McGovern Institute for Brain Research at MIT and one of the study’’s 13 authors.
He added that he hopes the research might lead to ways of predicting or monitoring individual patients” response to treatments for rare neurodegenerative disease.
Thus, they studied three carefully matched groups of 13 subjects each: schizophrenia patients, nonpsychotic first-degree relatives of patients and healthy controls. They selected patients who were recently diagnosed.
The subjects were scanned by functional magnetic resonance imaging (fMRI) while resting and while performing easy or hard memory tasks.
The researchers were especially interested in the default system, a network of brain regions whose activity is suppressed when people perform demanding mental tasks.
It was found that in the schizophrenia patients were less able than healthy control subjects to suppress the activity of this network during the task.
And Interestingly, the researchers found that the less the suppression and the greater the connectivity, the worse the patients performed on the hard memory task, and the more severe their clinical symptoms.
“We think this may reflect an inability of people with schizophrenia to direct mental resources away from internal thoughts and feelings and toward the external world in order to perform difficult tasks,” explained the authors.
The hyperactive default system could also help to explain hallucinations and paranoia by making neutral external stimuli seem inappropriately self-relevant.
The default system is also overactive, though to a lesser extent, in first-degree relatives of schizophrenia patients who did not themselves have the disease, which indicates that overactivation of the default system may be linked to the genetic cause of the disease rather than its consequences.
The study appears in the advance online issue of the Proceedings of the National Academy of Sciences. (ANI)

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