Functional and effective connectivity in neuroimaging: A synthesis

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Abstract
The brain appears to adhere to two principles of functional organization; functional segregation and functional integration. The integration within and between functionally specialized areas is mediated by functional or effective connectivity. The characterization of this sort of connectivity is an important theme in many areas of neuroscience. This article presents one approach that has been used in functional imaging.This article reviews the basic distinction between functional and effective connectivity (as the terms are used in neuroimaging) and their role in addressing several aspects of functional organization (e.g. the topography of distributed system, integration between cortical areas, time‐dependent changes in connectivity and nonlinear interactions). Emphasis is placed on the points of contact between the apparently diverse applications of these concepts and in particular the central role of eigenimages or spatial modes. Although the framework that has been developed is inherently linear, it has been extended to assess nonlinear interactions among cortical areas. ©1994 Wiley‐Liss, Inc.