Identification and characterization of the thalamic ventral posterior complex by 11.7T ex vivo diffusion tensor imaging.

The thalamic ventral posterior (VP) nuclear complex includes several subnuclei, including the VPM, VPL, VPI, and VMb, each with distinct inputs, axonal trajectories, and staining properties. Understanding the three-dimensional organization of neuronal fiber structures of the VP complex is crucial for understanding intra-thalamic and thalamocortical connections related to somatosensory processing. In this study, an ex vivo block of the human brain was scanned using mesoscopic Diffusion Tensor Imaging (DTI), and the four VP subnuclei were identified using existing histological atlases as references. The VP subnuclei were characterized using a mean diffusivity (MeanD) map, orientation-coded fractional anisotropy (FA) map, and tractography obtained from DTI. The results demonstrated differential patterns in MeanD and orientation-coded FA maps among the four subnuclei, underscoring the potential of mesoscale imaging to identify and differentiate these subnuclei. The tractography identified patterns of afferent and efferent fibers unique to each nucleus, offering insights into their functional roles in sensory processing. The findings highlighted the advantages of DTI in visualizing the direction of fibrous structures and conducting three-dimensional tractography, offering a foundation for further investigations into in vivo imaging applications and the neural mechanisms of somatosensory disorders, including central pain syndrome.