Methodological issues relating to in vivo cortical myelography using MRI.

The relationship between neocortical structure and function is a key area of research in neuroscience. Most studies of neural function, whether using neurophysiology or neuroimaging methods, are interpreted with relation to the underlying cortical myelo- and cytoarchitecture. For functional neuroimaging studies this often means using cytoarchitectonic maps based on the study of a limited number of brains, despite evidence for substantial interindividual variation. Improvements in MR technology, resulting in wider availability of high-field MRI systems, have led to an increase in the achievable resolution in MR scans. Several groups have reported the in vivo detection of myelination patterns within the cortex, consistent with those observed in postmortem tissue. This leads to the possibility of predefining areas for fMRI analysis based on the cortical architecture. To do this it is essential to know, in a quantitative way, how reliably myeloarchitectonic areas and boundaries can be detected using MRI. Here we investigate the striate cortex, known to be coincident with V1, to assess the detectability of the stria of Gennari across V1 and across subjects. Under optimal conditions, 80% of the stria of Gennari was visualized using our methodology, although there was considerable variability in the level of detection across subjects. We discuss the limitations of the methodology and propose ways to improve the detection level of cortical myeloarchitecture more generally.