Paul M. Thompson, Craig Schwartz, Robert T. Lin, Aelia A. Khan, Arthur W. Toga and Robert C. Collins
Laboratory of Neuro Imaging, Department of Neurology, Division of Brain Mapping, UCLA School of Medicine, Los Angeles, California 90095
Morphometric variance of the human brain is qualitatively observable in surface features of the cortex. Statistical analysis of sulcal geometry will help with multi-subject atlasing and other brain mapping projects. This investigation describes the variability in location of 5 sulci surveyed in each hemisphere of 6 post mortem human brains, placed within the Talairach stereotaxic grid. Whole human heads were prepared for sectioning with cryoprotectant, rapidly frozen, and blocked.
The heads were then cryosectioned at 50 micron intervals, and high-resolution 1024x1024 (24-bit) color images were acquired every 500 microns from the specimen blockface. Outlines of the following structures were directly identified at high magnification on sagittally resampled sections: the parieto-occipital sulcus, the anterior and posterior rami of the calcarine sulcus, the cingulate and marginal sulci, and the supracallosal sulcus. Outlines digitized at 20000 points per surface were reparametrized to allow surface comparisons. Statistics of 3-dimensional variation for arbitrary points on each surface were calculated locally, after placement of the standardized individual data within the Talairach stereotaxic grid. Average surfaces were computed for each sulcus, allowing local variability to be measured and visualized by adding a range of colors to the representation of each sulcal surface.
These findings indicate that macroanatomic individuality in the internal structure of the human brain cannot be adequately accounted for by stereotaxic coordinates alone. Such statistics on spatial variability, at important functional interfaces, will be a fundamental component of probabilistic atlases of the human brain.
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