Introduction

From birth to childhood, motor development has experienced important milestones. Such as vertical neck, sitting, standing, walking, and gradually implementing complex and fine functions³. At the same time, research have shown that sensorimotor exploration drives cognition¹. The CST is of paramount importance in the motor system, as it mediates voluntary distal movements. However, the motor development has laterality, such as hand function. Therefore, as an important fiber bundle reflecting motor function, the asymmetric development of CST is of great significance to the study of basic developmental rules and disease mechanisms. Asymmetry in CST development from birth to childhood has not yet been revealed. Is it born with birth? Based on this, our research aims to explore the asymmetry of CST development based on diffusion kurtosis imaging.

Methods

This study was approved by the local Internal Review Board and all parents of participants had signed the informed consents. For the inability to cooperate with the study subjects, the sedation was performed before the examination. The inclusion criteria were completed DKI examination and no significant abnormalities were observed in conventional magnetic resonance. Newborn asphyxia (5minApgar ≤ 7 points), hypoxic ischemic encephalopathy, central nervous system infection, epilepsy, developmental delay and other diseases that may affect the central nervous system are excluded.
Single-shot EPI diffusion kurtosis imaging was performed on a 3.0T scanner (General Electric Signa HDXT, WI, USA) with an eight-channel head coil. The other parameters were: b values = 500, 1000, 2000, 2500 s/mm²; 18 gradient directions; Repetition time/Echo time =11000/91.7 ms; thickness = 4 mm; FOV = 180 × 180 mm² ~ 240 × 240 mm²; acquisition matrix = 128 × 128 ~ 172 × 172. Diffusion and kurtosis tensors were estimated by using constrained weighted linear least squares. Fractional anisotropy (FA), Mean kurtosis(MK), Axonal water fraction (AWF), Tortuosity (TorT_I) were calculated according to the white matter model for DKI.
Use local template to register with JHU template to get templates and atles of different ages. Select CST_L and CST_R as regions of interests (ROI). Paired T test and non-parametric test are used to suggest CST_L and CST_R differences; The bar chart is used to show the difference between CST_L and CST_L. Tests were considered significant at P≤0.05.

Result

A total of 353 subjects were included. They are divided into seven groups according to the age of the examination: ≤28d,28d-6m,6-12m,1-2y,2-3y,3-6y,6-13y. (Table 1) Difference analysis between CST_L and CST_R: From 0-13 years old, the FA, MK, AWF and TorT_I of CST_L and CST_R were statistically significant, and showed left-sided dominance; But from birth to 6 months of age, only MK showed statistical difference.(Fig 1)

Discussion

This study used DKI to explore the asymmetry of CST development from neonate to childhood. Different from the previous hemispheric asymmetry research, our study subjects is the continuous stage from 0-13 years old. It is found that CST have hemispheric difference and left-hemisphere advantage. Although high variability exists between individuals, the left and right hemispheres of our brain display anatomical and molecular left-right asymmetries that correlate with their functional specialization in particular cognitive processes^4,5. The presence of left CST laterality after 6 months may be related to the development of motor function. For example, after 6 months of age, there are signs of hand grasping and standing.

Conclusion

From 0-13 years old, there is hemispheric asymmetry in the development of CST, and they show left-sided dominance; The CST hemispheric asymmetry does not exist at birth, but appears at 6 months. From birth to 6 months of age, the difference in laterality of CST was reflected in glial cell proliferation around the axon, but there was no difference in the axon itself.

Acknowledgements

This study was supported by the National Natural Science Foundation of China (81971581, 81901823, 81771810), National Key Research and Development Program of China (2016YFC0100300), the 2011 New Century Excellent Talent Support Plan of the Ministry of Education of China (NCET-11-0438), the Project Funded by China Postdoctoral Science Foundation (2019M653659), and the Natural Science Basic Research Plan in Shaanxi Province of China (2019JQ-198).