Radial correlation contrast--a functional connectivity MRI contrast to map changes in local neuronal communication

A functional connectivity MRI method that groups neighboring voxels in relation to their degree of temporal cross-correlation between their time courses is presented. This grouping generates a vector field, which is assumed to provide insights into the local organization of neuronal activity. Application with high spatial resolution fMRI rat data subjected to electric forepaw sensory stimulation (156 . 156 . 1000 micron1) shows a significant localized increase of the vector field amplitude in cortical layers 4 and 2/3 of the primary sensory cortex and in layer 2/3 of the primary motor cortex, suggesting a strong correlation with local neuronal communication. Vector field phases exhibit a transition with neuronal activation from random-like orientations during rest to clusters of common orientations. Cluster size is shown to be weakly dependent on the radii of the vector field calculation, and shuffling voxel position within clusters generates a random-like vector orientation instead. This suggests that changes in vector orientations upon activation represent changes in the internal correlation between voxels that is interpreted as a change in the internal neuronal communication.