Fig. 2 highlights the advantage of CBV-based fMRI for layer-fMRI applications with an example of the primary visual cortex. It can be seen how the CBV signal change is dominated from the middle cortical layers at the location of the Stria of Genari (green arrow). GE-BOLD signal, on the other hand, shows the largest signal peaks in the superficial layers, most probably due to unwanted signal spillage from deeper layers. The signal variations along the columnar dimension, however, does not seem to be that much affected by signal spillage. This might be coming from the fact that most of the larger intra-cortical veins are orthogonally-oriented to the cortical surface. These results suggest that the CBV-contrast is most vital to interpret single-contrast variations across cortical layers. For the interpretation of single-contrast columnar variations, a corresponding specificity advantage of CBV is less clear.
