After a brief review of our previous efforts exploring human primary visual cortex (V1) with high-resolution (sub-millimeter resolution) functional magnetic resonance imaging (fMRI) [1-5], I will present the results from three unpublished studies, all conducted on a 4 Tesla MRI system. In the first study, using both direct mapping and indirect decoding approaches, we demonstrated that orientation selectivity in human V1 can be relaibly revealed. In particular, we found that large drining veins contribute significantly to orientation-selective BOLD signals. These results are strikingly surprising and invite more detailed anatomical and functional studies of draining veins at various spatial scales. In the second study, we manupulated the spatial resolution of fMRI data and analyzed the geometric relationship between 1) the spatial resolution of imaging voxels, 2) the systematic increase and decrease in the proportion of direction-selective voxels, and 3) the repeatition periodicity of assumed underlying direction-selective hypercolumns in hMT+. Using this approach, we were able to indirectly estimate the average size of hypercolumns for motion direction in hMT+, which was approximately 0.7 mm in the narrow dimension. Finally, in the third study elucidating the object-selective responses in human occipito-temrpoal cortex, I will highlight the unique advantage of doing these experiments at higher resoutions.
[1] Cheng et al., Neuron 32, 359-374, 2001
[2] Sun et al., Nature Neuroscience 10, 1404-1406, 2007
[3] Tajima et al., Journal of Neuroscience 30, 3264-3270, 2010
[4] Cheng, NeuroImage 62, 1029-1034, 2012
[5] Sun et al., Cerebral Cortex 23, 1618-1629, 2013