The contribution of cortical thickness and surface area to gray matter asymmetries in the healthy human brain

Abstract

Human cortical gray matter (GM) is structurally asymmetrical and this asymmetry has been discussed to be partly responsible for functional lateralization of human cognition and behavior. Past studies on brain asymmetry have shown mixed results so far, with some studies focusing on the global shapes of the brain's surface, such as gyrification patterns, while others focused on regional brain volumes. In this study, we investigated cortical GM asymmetries in a large sample of right-handed healthy volunteers (n = 101), using a surface-based method which allows to analyze brain cortical thickness and surface area separately. As a result, substantially different patterns of symmetry emerged between cortical thickness and surface area measures. In general, asymmetry is more prominent in the measure of surface compared to that of thickness. Such a detailed investigation of structural asymmetries in the normal brain contributes largely to our knowledge of normal brain development and also offers insights into the neurodevelopmental basis of psychiatric disorders, such as schizophrenia.

Keywords: asymmetry; cortical thickness; cortical volume; lateralization; surface area.

Figure 1

Brain regions of significantly positive Laterality Index (LI) (leftward asymmetry) or negative LI (rightward asymmetry) in cortical volume (Bonferroni‐corrected, P < 0.0015). 3D models generated with 3Dslicer (http://www.slicer.org/). Red color = brain regions showing significant leftward asymmetry; blue color = brain regions showing significant rightward asymmetry. The results are shown on the left hemisphere. (a) lateral, (b) medial view, and (c) LI for cortical volumes of each brain region is displayed by histogram. * indicates significant LI increase or decrease controlling for age and gender in region‐specific analyses (Bonferroni‐corrected, P < 0.0015).

Figure 2

Brain regions of significantly positive LI (leftward asymmetry) or negative LI (rightward asymmetry) in cortical thickness (Bonferroni‐corrected, P < 0.0015). 3D models generated with 3Dslicer (http://www.slicer.org/). Red color = brain regions showing significant leftward asymmetry; blue color = brain regions showing significant rightward asymmetry. The results are shown on the left hemisphere. (a) lateral, (b) medial view, and (c) LI for cortical thickness of each brain region is displayed by histogram. * indicates significant LI increase or decrease controlling for age and gender in region‐specific analyses (Bonferroni‐corrected, P < 0.0015).

Figure 3

Brain regions of significantly positive LI (leftward asymmetry) or negative LI (rightward asymmetry) in cortical surface area (Bonferroni‐corrected, P < 0.0015). 3D models generated with 3Dslicer (http://www.slicer.org/). Red color = brain regions showing significant leftward asymmetry; blue color = brain regions showing significant rightward asymmetry. The results are shown on the left hemisphere. (a) lateral, (b) medial view, and (c) LI for surface area of each cortical region is displayed by histogram. * indicates significant LI increase or decrease controlling for age and gender in region‐specific analyses (Bonferroni‐corrected, P < 0.0015).