The relationships of the “primary” cytoarchitectonic neocortical fields, 17, 41, 3b, and 4 (Brodmann areas), to salient topographic landmarks have been reconstructed from serial histological sections in 20 human cerebral hemispheres (10 brains). Each of these architactonic fields is found to boar a characteristic relationship to a set of enframing anatomic landmarks, in particular, gyri, fissures, and sulci, that can be readily defined by MRI. Two classes of variability were found characteristic, at least to some extent, of each of the fields. Class 1 variability—variability that is not predictable from visible landmarks—was typical of the polar and for the cuneal and lingual oxtracalcarino distributions of field 17 and the distribution of field 4 upon the paracentrel lobule. Class 2 variability—variability that is closely predictable from visible landmarks—is seen in the marked intenndividual or interhemisphenc variation in size or shape of a field and was found to be prominent for all four fields. Because of the prominence of class 2 variability, direct reference to the landmarks that frame these fields may he expected to be a more reliable basis for functional mapping than reference to a template or tereotactic coordinate-based system of reference to a standard or idealized brain.

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