GYRI OF THE HUMAN NEOCORTEX - AN MRI-BASED ANALYSIS OF VOLUME AND VARIANCE

This magnetic resonance imaging (MRI)-based morphometric analysis of c ortical topography in the human brain is based upon the segmentation a nd parcellation of volumetric T1-weighted MRI data for a set of 20 you ng adult brains including 10 males and 10 females. For the most part, each parcellation unit (PU) of the neocortex corresponds to a single o r a portion of a single gyrus. The volumes of each PU were computed fo r each brain. Subsets of PUs were also grouped so as to represent the neocortex for the frontal, temporal, parietal and occipital lobes. The coefficient of variation of the mean volume of total neocortex and th at of the neocortex assigned to individual lobes cluster around 10%. w hereas that of neocortex assigned to the individual gyri (PU) is more than twice that value. Approximately 80% of the total variance in gyra l volume arises from determinants interactive for individual and speci fic gyri, while only similar to 10% of the total Variance appears to b e a reflection of uniform scaling to total neocortical volume. Sexual dimorphism contributes a pervasive though relatively small component o f this variance. These results have implications for the study of stru cture-function correlation, and the proper statistical methods of hand ling volumetric data in morphometric studies. In addition, the nature of the covariance structure of the data will lead to future hypotheses regarding the relationships between the various potential genetic and epigenetic gyral influencing factors.