Layer Dependence of Monocular and Binocular Responses in Human Ocular Dominance Columns at 7T using VASO and BOLD

The neurons located in the striate cortex (V1) preferentially respond to the input from one eye or another, forming a fingerprint-like pattern of ocular dominance columns (ODCs). At this mesoscopic scale, accessible by ultra-high field fMRI, V1 is supplied/drained by a network of surface (pial) vessels that connect to descending/ascending tangential vessels that penetrate the cortex and supply/drain a capillary bed whose density is also layer dependent. In this study, we measured the layer dependence of monocular and binocular responses of ocular dominance columns in V1 at 7T using Blood Oxygenation Level Dependent (BOLD) and VAscular Space Occupancy (VASO) contrasts. Our results indicate that the microvascular blood volume changes that give rise to VASO are well confined to the site of neural activity across the layers of the cortex and between the columns. Pial veins dominate the BOLD response and mix the signal between columns. When the GRE BOLD response was examined in only the VASO specific voxels (thus eliminating the pial vein signal), the laminar profile was very similar to VASO, however, the columnar response was still blurred. Caution needs to be exercised in the interpretation of signal changes in BOLD at the mesoscale both in terms of feedforward/feedback effects and inhibitory and excitatory effects. Highlights- VASO produced laminar profiles that were consistent with the known layer-dependent neuronal response to monocular and binocular stimulations. - VASO better differentiated the response between columns belonging to the left and right eyes. - GRE BOLD signal spatial specificity was poor in both laminar and columnar directions, however, when the pial veins were suppressed, the laminar BOLD signal was very similar to the VASO signal. - Caution needs to be exercised when interpreting cognitive neuroscience BOLD studies at the mesoscale level due to the confounding effects of pial and sub-pial veins and venules.