Spatial specificity of CBF and BOLD responses induced by neural activity

Functional magnetic resonance imaging (fMRI) has been widely utilized for imaging brain functions. However, the extent of the fMRI response around the active sites, at sub-millimeter columnar resolution, remains poorly understood. We have investigated spatial specificity of conventional positive blood-oxygenation level dependent (BOLD), early negative BOLD, and perfusion-based fMRI by using a well-established feline orientation column model. The conventional positive BOLD signal is widespread and diffused due to large venous vessel contributions. However, both the early negative BOLD and cerebral blood flow (CBF) responses are specific to individual cortical columns. Thus, hemodynamic-based fMRI can indeed be used to map individual functional columns if large vessel contributions can be minimized.