MRI-Based topographic parcellation of human cerebral white matter and nuclei II. Rationale and applications with systematics of cerebral connectivity.

We describe a system for parcellation of the human cerebral white matter and nuclei, based upon magnetic resonance images. An algorithm for subdivision of the cerebral central white matter according to topographic criteria is developed in the companion manuscript. In the present paper we provide a rationale for this system of parcellation of the central white matter and we extend the system of cerebral parcellation to include principal subcortical gray structures such as the thalamus and the basal ganglia. The volumetric measures of the subcortical gray and white matter parcellation units in 20 young adult brains are computed and reported here as well. In addition, with the comprehensive system for cerebral gray and white matter structure parcellation as reference, we formulate a systematics of forebrain connectivity. The degree to which functionally specific brain areas correspond to topographically specific areas is an open empirical issue. The resolution of this issue requires the development of topographically specific anatomic analyses, such as presented in the current system, and the application of such systems to a comprehensive set of functional-anatomic correlation studies in order to establish the degree of structural-functional correspondence. This system is expected to be applied in both cognitive and clinical neuroscience as an MRI-based topographic systematics of human forebrain anatomy with normative volumetric reference and also as a system of reference for the anatomic organization of specific neural systems as disrupted by focal lesions in lesion-deficit correlations. Copyright 1999 Academic Press.