OCULAR DOMINANCE IN HUMAN V1 DEMONSTRATED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING

Very high resolution functional magnetic resonance imaging (fMRI) at a 4 Tesla (T) magnetic field was used to map ocular dominance regions i n the human visual cortical layers using the blood oxygen level depend ent (BOLD) contrast mechanism. The fMRI response from primary visual c ortex (V1) exhibited a distribution of ocular dominance reminiscent of the single-cell recordings of Hubel and Wiesel. Pixels could be group ed into seven categories varying from left-only response to binocular- only response to right-only responses. Nonspecific responses were foun d in the MRI-visible draining veins as well as in the parenchyma. Alth ough large vessel BOLD signals are easily detectable, regard less of f ield strength, they demonstrate a MRI response to photic input that co uld not be used to distinguish ocular dominance. The difference in BOL D response between a region activated by one eye and that activated by the other is only 2.9% on average. This necessitates the use of a dif ference paradigm to visualize the regions of ocular dominance accurate ly. The data show that BOLD-based fMRI is sensitive to neuronal activi ty in cortical columns when using differential techniques, opening up the possibility of mapping specialized populations of neurons in human s that are not accessible to electrophysiological or other methods of invasive mapping.