Cortical microstructure and hemispheric specialization – a diffusion-imaging analysis in younger and older adults
Authors: Wróbel Paweł P. , Braaß Hanna , Frey Benedikt M. , Bönstrup Marlene , Guder Stephanie , Frontzkowski Lukas K. , Feldheim Jan F. , Cheng Bastian , Rathi Yogesh , Pasternak Ofer , Thomalla Götz , Koerte Inga K. , Shenton Martha E. , Gerloff Christian , Quandt Fanny , Higgen Focko L. , Schulz Robert 
Published: December 2023

Characterizing cortical plasticity becomes increasingly important for identifying compensatory mechanisms and structural reserve in the aging population. While cortical thickness (CT) largely contributed to systems neuroscience, it incompletely informs about the underlying neuroplastic pathophysiology. In turn, microstructural characteristics may correspond to atrophy mechanisms in a more sensitive way, indicating a potentially necessary paradigm shift in neuroimaging. Fractional anisotropy (FA), a diffusion tensor imaging (DTI) measure, is inversely related to cortical histologic complexity. Axial (AD) and radial diffusivity (RD) are assumed to be linked to density of structures oriented perpendicular and parallel to cortical surface respectively. We hypothesized (1) that cortical DTI will reveal microstructural correlates for hemispheric specialization, particularly in the language and motor systems and (2) that lateralization of cortical DTI parameters will show an age effect, paralleling age-related changes in activation, especially in the prefrontal cortex. We re-analyzed data of healthy younger and older adult participants (n=91). DTI measures and CT were extracted from Destrieux atlas regions. Diffusion measures showed lateralization in specialized motor, language, visual, auditory, and inferior parietal cortices. Age-dependent increased lateralization was observed for DTI measures in the prefrontal, angular, superior temporal, and lateral occipital cortex. CT did not show any age-dependent alterations in lateralization. Our observations argue that cortical DTI is able to capture correlates of microstructural properties associated with functional specialization, resembling findings from histology. Age effects on diffusion measures in the integrative prefrontal and parietal areas may shed novel light on the atrophy-related plasticity in healthy aging.

Significance statement

Cortical thickness significantly contributed to systems neuroscience research related to cortical neuroplasticity. However, regarding the underlying cortical microstructure it remains an unspecific measure. With a strong lateralization in diffusion measures but not in thickness in specialized areas we demonstrate that cortical diffusion MRI is suitable to grasp microstructural features linked to specialization already described in histology literature. The findings in the lateralization of prefrontal and parietal cortical features may reflect age-related dynamic in cerebral activation. These results indicate the great potential of cortical diffusion tensor imaging in neuroscience and may even emphasize a necessary paradigm shift from the assessment of cortical macrostructure towards cortical microstructure for a better understanding of neuroplasticity and structure-function relationships in health and disease.