Interactions among neuronal systems assessed with functional neuroimaging

Cortical organisation is based on the principles of functional specialisati on and functional integration. Those two concepts exist at multiple spatial scales. For example at a macroscopic level, functionally segregated areas V1 and V5 are integrated within the dorsal visual stream. At a microscopic level, it is possible to infer the functional integration of (segregated) o cular dominance columns within area V1. At the macroscopic level functional specialisation and integration can be tested with functional neuroimaging, using fMRI/PET or EEG/MEG. A framework that allows making inferences on fu nctional integration between brain regions using fMRI will be presented. Th e common feature of all techniques within that framework is that they can i ncorporate second order terms and therefore explicitly allow for contextual modulations. Two examples demonstrate how attention and paired associates learning can modulate effective connectivity within the visual system. Furt hermore these models can incorporate non-linear modulatory (feedback) conne ctions that can account for the changes in effective connectivity observed.