Heritability of the limbic networks

Abstract

Individual differences in cognitive ability and social behaviour are influenced by the variability in the structure and function of the limbic system. A strong heritability of the limbic cortex has been previously reported, but little is known about how genetic factors influence specific limbic networks. We used diffusion tensor imaging tractography to investigate heritability of different limbic tracts in 52 monozygotic and 34 dizygotic healthy adult twins. We explored the connections that contribute to the activity of three distinct functional limbic networks, namely the dorsal cingulum ('medial default-mode network'), the ventral cingulum and the fornix ('hippocampal-diencephalic-retrosplenial network') and the uncinate fasciculus ('temporo-amygdala-orbitofrontal network'). Genetic and environmental variances were mapped for multiple tract-specific measures that reflect different aspects of the underlying anatomy. We report the highest heritability for the uncinate fasciculus, a tract that underpins emotion processing, semantic cognition, and social behaviour. High to moderate genetic and shared environmental effects were found for pathways important for social behaviour and memory, for example, fornix, dorsal and ventral cingulum. These findings indicate that within the limbic system inheritance of specific traits may rely on the anatomy of distinct networks and is higher for fronto-temporal pathways dedicated to complex social behaviour and emotional processing.

Keywords: cingulum; diffusion tractography; fornix; heritability; limbic system; uncinate fasciculus.

Fig. 1.

Dissected dorsal (blue) and ventral (yellow) components of the cingulum bundle. The vertical midline of the splenium of the corpus callosum separates the uppermost anterior coronal slices of the dorsal cingulum from the lowermost slices of the ventral cingulum. When the width of the splenium is an even number of voxels and cannot be halved easily, the consistent method is to select the first voxel of the posterior half of the splenium. This slice is included in the dorsal cingulum ROI (blue).

Fig. 2.

Representative examples of the four limbic tracts dissected in MZ and DZ twin pairs. The dorsal cingulum is shown in blue, the ventral cingulum in yellow, the fornix in red and the uncinate fasciculus in green colour.

Fig. 3.

The relative contribution (in percentages) of genetic (A), shared environmental (C) and specific environmental (E) factors on the variability of the FA, MD and volume of fornix (red), the bilateral dorsal (blue) and ventral (yellow) cingulum, and the bilateral uncinate fasciculus (green).