Genetics of Anisotropy Asymmetry: Registration and Sample Size Effects

Abstract

Abstract. Brain asymmetry has been a topic of interest for neuroscientists for many years. The advent of diffusion tensor imaging (DTI) allows researchers to extend the study of asymmetry to a microscopic scale by examining fiber integrity differences across hemispheres rather than the macroscopic differences in shape or structure volumes. Even so, the power to detect these microarchitectural differences depends on the sample size and how the brain images are registered and how many subjects are studied. We fluidly registered 4 Tesla DTI scans from 180 healthy adult twins (45 identical and fraternal pairs) to a geometrically-centered population mean template. We computed voxelwise maps of significant asymmetries (left/right hemisphere differences) for common fiber anisotropy indices (FA, GA). Quantitative genetic models revealed that 47-62% of the variance in asymmetry was due to genetic differences in the population. We studied how these heritability estimates varied with the type of registration target (T1-or T2-weighted) and with sample size. All methods consistently found that genetic factors strongly determined the lateralization of fiber anisotropy, facilitating the quest for specific genes that might influence brain asymmetry and fiber integrity.

Genetic influences on brain asymmetry: A DTI study of 374 twins and siblings

“…In our prior work (Jahanshad et al, 2009), we found that using T2-weighted images for registration purposes yields results similar to those obtained from using higher resolution T1-weighted images, with the advantage that they are inherently in register with the diffusion-weighted images from the same scanning session. To further ensure alignment of the white matter regions of interest, in this study, we decided to use a DTI-derived measure, the FA, to drive the registration.…”