MR imaging in the non-human primate: studies of function and of dynamic connectivity.

Since its early development in the late 1940s, nuclear magnetic resonance has become a powerful tool for applications ranging from chemical analysis or the study of the structure of solids to biomedical investigations. In the early 1990s the potential of this technique for functional brain mapping was demonstrated, causing unprecedented excitement in both basic and clinical neuroscience. It was shown that by using the appropriate pulse sequences the so-called functional magnetic resonance imaging (fMRI) technique can be made sensitive to local magnetic susceptibility alterations produced by changes in the concentration of deoxyhemoglobin in venous blood vessels. This blood-oxygenation-level-dependent (BOLD) contrast mechanism was successfully implemented in awake human subjects, in small animals, and recently in the non-human primate--the experimental animal of choice for the study of cognitive behavior. Simultaneous imaging and electrode recordings promise new insights into the mechanisms by which large-scale networks in the brain contribute to the local neural activity recorded at a given cortical site. Moreover, the use of MRI-visible tracers and of electrical microstimulation applied during imaging proves to be ideal for the study of connectivity in the living animal.