1NIH, Bethesda, MD, United States; 2National Institutes of Health, Bethesda, MD, United States
Channelrhodopsins (ChRs) were expressed along thalamocortical and cortiocortical pathways in the rat brain. An implanted fiber optic was targeted to axonal fibers that input neural activity into cortical areas. This experimental design allowed us to control projection activity in a fiber-specific manner and to detect reliable fMRI signals at relatively low light intensities in cortex remote from the fiber optic-penetrated brain areas. Light-driven fMRI signal can also be detected due to antidromic activity from back-propagated action potentials. This work demonstrated the usefulness of fMRI to detect brain activation via optogenetics of specific neural fiber pathways.