Effective connectivity and neuroimaging

In the past decade functional neuroimaging has been extremely successful in establishing functional segregation as a principle of organisation in the human brain. Functional segregation is usually inferred by the presence of activation foci in change or statistical parametric maps. The nature of the functional specialisation is then attributed to the sensorimotor or cognitive process that has been manipulated experimentally. Newer approaches have addressed the integration of functionally specialised areas through characterising neurophysiological activations in terms of distributed changes (e.g. McIntosh et al 1994a, Friston et al 1993a, Friston et al 1993b, Lagreze et al 1993, McIntosh & Gonzalez-Lima 1991, Horwitz et al., 1995; Horwitz and Sporns, 1994). These approaches have introduced a number of concepts into neuroimaging (e.g. functional and effective connectivity, eigenimages, spatial modes, information theory, multidimensional scaling) and their application to issues in imaging neuroscience (e.g. functional systems, cortical integration, associative plasticity, and nonlinear cortical interactions). The study of effective connectivity will also gain importance for relating cognitive theories (eg. attention) to brain operations. For example categorical comparisons of functional brain imaging data suggests modulation of extrastriate cortical responses by attentional processes (Corbetta et al 1991). It would be very compelling to demonstrate the modulation of responsiveness of these areas in terms of attention-dependent changes in the interactions or effective connectivity among.