Dendritic spine density in the default mode network : a postmortem morphometric pilot study of schizophrenia
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Neuroimaging studies have found decreased activity and functional connectivity within and between brain regions in subjects with schizophrenia. These findings correlate with a decline in dendritic spine density in the corresponding areas, especially in prefrontal regions. Schizophrenia is therefore generally associated with a decrease in functional and structural connectivity. However, in regions associated with the default mode network (DMN) subjects with schizophrenia consistently demonstrate abnormally increased activity and internal functional connectivity, disagreeing with the notion that schizophrenia is a disconnection syndrome. The structural basis for this hyperactivity and hyperconnectivity remains uncertain. The objective of the present study was to investigate structural connectivity at the synaptic level in the main regions of the DMN. Dendritic spine density on Golgi-impregnated layer III pyramidal neurons in the functional hubs of the DMN, the medial prefrontal cortex (MPFC) and the posterior cingulate cortex (PCC), from medication-naïve schizophrenic subjects was examined. The results of the study indicated regional variations in spine density within the DMN, with the MPFC showing significantly higher spine density compared to the PCC. As opposed to other studies on healthy subjects, the results of the study indicated that dendritic spine density was abnormally increased in the DMN in schizophrenia. The findings of the present study suggest that the increased activity and functional connectivity of the DMN is coupled with increased structural connectivity.