INDIVIDUAL VARIATION OF CORTICAL SURFACE-AREA ASYMMETRIES

Asymmetries in the size of cortical regions are regularly associated w ith functional lateralization. Assessment of cortical asymmetry is oft en confounded by measurement artifact and a lack of information about the normal variance of asymmetry in regions that are functionally symm etric. In order to measure hemispheric asymmetries in the surface area of cortical gyri, magnetic resonance (MR) images were acquired from 1 0 normal, right-handed males. Computer representations of the cortical surface in all 20 hemispheres were reconstructed from the images by f irst creating a white matter model and then 'inflating' it to approxim ate the cortical surface. The advantage of this approach is that it ac curately models the deep sulci as well as the cortical surface. Surfac e area measurements of the whole hemisphere, the postcentral and the c ingulate gyrus were collected from each subject. For each region an as ymmetry score was computed based on the difference in the surface area of the left and right regions. Many subjects showed asymmetries in th ese two gyri; however, the mean asymmetry scores were never significan tly asymmetric. The large variability of individual asymmetry scores i ndicates that cortical asymmetries may be present even in the absence of clear functional asymmetry. An understanding of the degree of asymm etry in structures that do not show clear functional lateralization is critical for interpreting data gathered from cortical regions that ar e functionally asymmetric.