Commentary: Microstructure, length, and connection of limbic tracts in normal human brain development

Citation: Oishi K (2017) Commentary: Microstructure, length, and connection of limbic tracts in normal human brain development. Limbic tracts are affected in various neurological and psychiatric diseases/disorders (Bogerts et al. The onset of the abnormality is of particular interest since many psychiatric disorders are known to have genetic backgrounds that might result in a specific phenotype of the brain anatomy (endophenotype) before the onset of the symptoms (Menzies et al. There is the potential that such endophenotypes could be detected even in very early developmental stages, therefore, quantification of the developmental status of the limbic fibers might be useful for identifying groups at high-risk for developing psychiatric disorders in the future. However, little is known about the normal developmental trajectories of these fiber tracts from a neonatal age to young adulthood, which is essential for the evaluation of a pathological deviation from normal brain development (Oishi et al., 2013). MRI scans are particularly challenging in subjects less than 4 years of age without sedation (Oishi et al., 2012), and therefore, establishing the normal developmental trajectory of this age-range will be an important asset for research communities(Oishi et al., 2011; Akazawa et al., 2015; Chang et al., 2016). Yu and his colleagues aimed to identify the normal developmental characteristics of the limbic fibers (Yu et al., 2014). They used diffusion tensor imaging (DTI) to characterize the microscopic, anatomical features of the live human brain from the neonatal period to 25 years of age, based on cross-sectional observation of 65 healthy individuals. Diffusion property, length, and anatomical connections of the three limbic tracts were evaluated: The cingulate gyrus part of the cingulum (cgc); the hippocampal part of the cingulum (cgh); and the fornix. The tracts-of-interest (TOI) approach was applied to accurately identify the white matter tracts and has been used to evaluate the microscopic status of the developing brain. Tractography was also used to measure the length of the limbic tracts, as well as to evaluate the connectivity of the anatomical structures that are related to the default mode network (DMN), which is defined by resting-state fMRI. In adult brains, the limbic fibers are known to connect the DMN-related structures. However, the role of these limbic fibers in connecting DMN structures has been unclear in early development.