Rs. Menon et al., OCULAR DOMINANCE IN HUMAN V1 DEMONSTRATED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING, Journal of neurophysiology, 77(5), 1997, pp. 2780-2787
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.