High-resolution MRI reflects myeloarchitecture and cytoarchitecture of human cerebral cortex

Maps of cytoarchitectonically defined cortical areas have proven to be a valuable tool for anatomic localization of activated brain regions revealed by functional imaging studies. However, architectonic data require observations in a sample of postmortem brains. They can only be used reliably for comparison with functional data as probabilistic maps after spatial normalization to a common reference space. The complete architectonic analysis of an individual living brain has not been achievable to date, because the relationship remains unclear between laminar gray value changes of cerebral cortex in magnetic resonance (MR) images and those of cyto- and myeloarchitectonic histologic sections. We examined intensity profiles through the cortex in five imaging modalities: in vivo T1 and postmortem T2 MRI, one cell body stain, and two myelin stains. After visualizing the dissimilarities in the shapes of these profiles using a canonical analysis, differences between the profiles from the different image modalities were compared quantitatively. Subsequently, the profiles extracted from the in vivo T1-weighted images were estimated from profiles extracted from cyto- and myeloarchitectonic sections using linear combinations. We could verify statistically the mixed nature of the cortical T1 signal obtained in vivo: The MR intensity profiles were significantly more similar to myeloarchitectonic than to cytoarchitectonic profiles, but a weighted sum of both fitted the T1 profiles best.