The relationship within and between the extrinsic and intrinsic systems indicated by resting state correlational patterns of sensory cortices

Much Research has been done on extrinsic and intrinsic systems, which consist of brain regions associated with the processing of externally and internally oriented stimuli, respectively. However, understanding of the underlying relationships within and between these two systems is relatively limited. To improve our understanding of these underlying relationships, we investigated the positive and negative correlations of three regions of interest (ROIs) located in the auditory, visual and somatosensory systems by using resting state functional MRI (fMRI) with a large sample size. We found that all three sensory systems exhibited significant negative correlation with the intrinsic system. In contrast, positive correlations between these sensory cortices and brain regions outside their respective system were limited. The present study extended former findings by indicating that multiple subsystems rather than a single subsystem of the extrinsic system are inherently negatively correlated with the intrinsic system. We suggest that these negative correlations between the extrinsic and intrinsic systems may explain the phenomenon that externally and internally oriented processes can always disturb or even interrupt each other. (c) 2007 Elsevier Inc. All rights reserved.