Mapping cortical columnar structures using fMRI.
Mapping cortical columnar structures is important to understand cortical information processing. To map submillimeter columnar structures noninvasively, we have evaluated various functional magnetic resonance imaging (fMRI) techniques using a well-established feline orientation column model. The conventional positive blood oxygenation level-dependent (BOLD) signal is widespread and diffuse due to large venous vessel contributions, resulting in its poor specificity to columns. However, the early-negative BOLD signal is induced by the early oxygen consumption increase without significant change in blood flow. This negative signal has been successfully applied for columnar mapping. Tissue-specific cerebral blood flow (CBF) response is also specific to individual cortical columns, suggesting that parenchyma-specific fMRI techniques are capable to map individual single-condition functional cortical columns in animals as well as humans.