The “default mode,” or baseline condition when the brain is idling, is not properly coordinated in patients with schizophrenia and this aberrant activity may be caused by poor connectivity between brain networks, a Yale School of Medicine researcher reports.
Co-author Godfrey Pearlson, M.D., professor of psychiatry, said he and his colleagues found that regions of the brain known previously to be individually abnormal in patients with schizophrenia, also function abnormally in concert in the default mode network.
“In addition, the extent of the default mode abnormalities correlated with the severity of auditory hallucinations, delusional thoughts, and attention deficits that are hallmarks of schizophrenia,” Pearlson said.
Although the exact role of the default network is unknown, it is thought to involve response to stimuli as well as self-referential and reflective activity that includes memory retrieval, inner speech, mental images, emotions, and planning of future events.
Schizophrenia is a psychotic disorder that alters patients’ perception, thought processes, and behavior as evidenced by hallucinations, delusions, disorganized speech or behavior, social withdrawal, and varied cognitive deficits. Episodic memory and attention are significantly impaired in schizophrenia.
A central feature of schizophrenia is disturbed integration of activity across multiple brain regions, or dysfunctional connectivity between frontal temporal brain regions. Symptoms of schizophrenia have been attributed to a failure of functional integration or aberrant connectivity among regions or systems of the brain.
The study included 21 patients with schizophrenia and 22 healthy subjects. The group performed a straightforward task while undergoing functional magnetic resonance imaging in which they were asked to detect an infrequent target sound within a series of standard and novel sounds. In the healthy subjects, the default mode network resonated slowly and regularly as observed by blood flow. In the patients with schizophrenia, the activity in the brain increased and was significantly more irregular, although they performed equally well on the task.
Abigail Garrity of Trinity College was the lead author and Vince Calhoun of the Institute of Living/Hartford Hospital was the senior author. Co-authors included Dan Lloyd of Trinity College and Kristen McKiernan and Kent Kiehl of the Institute of Living/Hartford Hospital.
The study was supported by, among other funders, the National Institutes of Health in a MERIT grant to Pearlson.
Reference: American Journal of Psychiatry 164: 450-457 (March 2007)
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