The individuality of shape asymmetries of the human cerebral cortex

Abstract

Asymmetries of the cerebral cortex are found across diverse phyla and are particularly pronounced in humans, with important implications for brain function and disease. However, many prior studies have confounded asymmetries due to size with those due to shape. Here, we introduce a novel approach to characterize asymmetries of the whole cortical shape, independent of size, across different spatial frequencies using magnetic resonance imaging data in three independent datasets. We find that cortical shape asymmetry is highly individualized and robust, akin to a cortical fingerprint, and identifies individuals more accurately than size-based descriptors, such as cortical thickness and surface area, or measures of inter-regional functional coupling of brain activity. Individual identifiability is optimal at coarse spatial scales (~37 mm wavelength), and shape asymmetries show scale-specific associations with sex and cognition, but not handedness. While unihemispheric cortical shape shows significant heritability at coarse scales (~65 mm wavelength), shape asymmetries are determined primarily by subject-specific environmental effects. Thus, coarse-scale shape asymmetries are highly personalized, sexually dimorphic, linked to individual differences in cognition, and are primarily driven by stochastic environmental influences.

Mode-based morphometry: A multiscale approach to mapping human neuroanatomy

“…(2) on the sphere, degenerate solutions exist, such that certain eigenmodes will have the same number of nodal lines and wavelengths, and they can be aggregated into an eigengroup l , similar to the angular momentum number in quantum physics. Each eigengroup comprises 2 l + 1 eigenmodes, and its wavelength is [46, 41] where R s is the radius of the sphere (see Table S1 for an explicit list of wavelengths and eigenmode membership for each eigengroup on a sphere of R s = 67 mm [41, 15]). Therefore, the eigenmodes of the cortical surface belonging to a given eigengroup have approximately the same spatial scale or wavelength given by Eq.…”

“…(2) on the sphere, degenerate solutions exist, such that certain eigenmodes will have the same number of nodal lines and wavelengths, and they can be aggregated into an eigengroup l, similar to the angular momentum number in quantum physics. Each eigengroup comprises 2l `1 eigenmodes, and its wavelength is [46,41] wavelength " 2πR s a lpl `1q ,…”

“…where R s is the radius of the sphere (see Table S1 for an explicit list of wavelengths and eigenmode membership for each eigengroup on a sphere of R s " 67 mm [41,15]). Therefore, the eigenmodes of the cortical surface belonging to a given eigengroup have approximately the same spatial scale or wavelength given by Eq.…”

“…Note that β j is distinct from the eigenvalue λ j , with the former corresponding to the contribution of eigenmode j to the t-map and the latter corresponding to the wavelength of eigenmode j. In this work, we considered N " 150 modes spanning wavelengths ě34 mm, given recent work showing that the most salient aspects of brain function reside at spatial wavelengths longer than 34 mm [15,41]. However, our results do not change with other choices of N (see Fig.…”

“…Indeed, recent work using geometric eigenmodes suggests that virtually all task-evoked activation maps obtained with functional MRI result from excitations of low-frequency modes spanning wavelengths > 60 mm [15]. Other work indicates that individual differences in brain anatomy are most salient at relatively coarse scales, spanning wavelengths ⩾37 mm [41]. Such findings challenge classical approaches to brain mapping that focus on identifying focal effects in isolated brain regions and underscore the benefits of a spatially-informed, multiscale approach.…”