Novel Methods for the Visualization and Analysis of Functional Maps in Cortex

Flat Maps 15 Oxyhemoglobin does not show this property [Raichle, 2000 #23]. It is diamagnetic (a material that is slightly repelled by a magnet is called diamagnetic; low negative susceptibility). An increasing oxyhemoglobin-deoxyhemoglobin ratio due to increased activity causes that the blood becomes more diamagnetic. This leads to a reduction in intravoxel dephasing [Demb, Figure 5: BOLD fMRI measures neural activity indirectly A: Control State. The arterial supply is fully oxygenated. The venous oxygenated- to-deoxygenated blood ratio is 60:40; B: Active State. The arterial blood flow is increased. The brain’s consumption of oxygen also increases, but by an amount, that does not fully compensate the increased arterial blood flow. Therefore, the proportion of oxygen in the venous return increases; Adapted from: [Wandell, 1999 #16] p.148