Several groups have now used human MRI to image the visual cortex at high resolution to identify the stria of Gennari ( Barbier, et al., 2002 Clark, Courchesne, & Grafe, 1992 Walters et al., 2003). Although this myeloarchitecture has been identified in postmortem tissue for over two centuries (Gennari, 1782), it is only recently that visualization has become possible in vivo. It can be distinguished from neighboring regions by the presence of the stria of Gennari, a thick band of myelination in layer 4B. The striate cortex, or Brodmann’s area 17, occupies a large region of the occipital lobe along the calcarine sulcus. The development of very high-resolution structural MRI may permit the definition of cortical areas based on myeloarchitecture when functional definition is not possible.Īlthough widely used, it has not been possible to measure, for an individual subject, how these functionally defined visual areas compare to anatomically defined regions of occipital cortex. This is the first demonstration that the definition of V1 by fMRI closely matches the anatomically defined striate cortex in the human brain. Intensity profiles taken through the gray matter on the V1 and V2 sides of the functional border indicate a measurable difference in the size of the hypointense band for all subjects. The band was identified in between 81% and 33% (mean 57%) of V1 defined using fMRI, and less than 5% of the identified band was in cortex outside V1. The anatomical signature of V1 was determined by the presence of a hypointense band in the middle of the cortical gray matter. In three separate scanning sessions, anatomical images were collected at three different slice orientations (300 μm × 300 μm, slice thickness, 1.5 mm). Functional borders were mapped with functional magnetic resonance imaging (fMRI) using a narrow, vertical black and white contrast-reversing wedge. We independently investigated the anatomical and functional borders between primary and secondary human visual areas (V1 and V2) in vivo. Recent successes in high-resolution magnetic resonance imaging of myeloarchitecture patterns in the cortex suggest that it may now be possible to compare directly human anatomy and function in vivo. The cerebral cortex has both anatomical and functional specialization, but the level of correspondence between the two in the human brain has remained largely elusive.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |