medwireNews: A neuroimaging study suggests that patients with schizophrenia have difficulty deactivating the default mode network (DMN), rather than having increased absolute metabolic activity.
Using arterial spin labeling (ASL), Jochen Kindler (University of Bern, Switzerland) and team found that schizophrenia patients had increased connectivity in the DMN, the network that is active at rest and deactivated during goal-oriented activity. The increased connectivity, which was centered in the precuneus, correlated with patients’ scores on the Positive And Negative Symptom Scale.
But contrary to the team’s expectations, it was not accompanied by increased cerebral blood flow (CBF).
The increase in DMN connectivity is in line with previous findings from blood oxygen level-dependent (BOLD) functional connectivity studies. Kindler et al note that BOLD analysis measures blood perfusion relative to other areas of the brain, whereas ASL gives an absolute CBF value. This means that data from BOLD studies do not show whether the increased DMN connectivity is caused by an absolute increase in metabolic activity.
Previous research in healthy people has shown functional connectivity and CBF in the DMN to be tightly coupled. But in the current study, which involved 27 patients with schizophrenia, seven with schizoaffective disorder, and 27 age- and gender-matched controls, increased connectivity in the precuneus of the patients was not associated with increased CBF. Indeed, controls had a slight, nonsignificant increase in CBF relative to controls.
Patients did have altered CBF in other areas; it was significantly reduced, relative to controls, in frontal and temporal areas, as well as the cuneus, inferior occipital gyrus, caudate, anterior cingulate, and lingual, postcentral, and fusiform gyri.
Overactivity of the DMN is thought to contribute to misattribution of thoughts in patients with schizophrenia. The researchers say this could be due to failure to reduce DMN activity relative to its resting state (ie, decreased responsiveness) or to an absolute increase in at-rest DMN activity.
“Because our data showed no elevation of CBF during rest, this study supports the first hypothesis,” they conclude in Schizophrenia Bulletin.
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