Critical Review and Comparison of Axonal Structures in MRI/DTI and Histology

Traditionally, our view of the connectivity in the human brain mostly relies on analogies to findings in other species, gross morphological observations, and functional studies. Direct visualization of connections in the human brain has been limited to very few tracing techniques which could be applied postmortem. Recent advances in diffusion MR opened new perspectives to study the human connectome. However, the anatomical basis of signals in diffusion MR and the limitations of these techniques at different spatial resolutions need to be better understood. To this end, ex vivo approaches combining high-resolution diffusion MR and histological fiber tracing techniques offer great potential to gain more insight into the limits and advantages of diffusion MR. The results of such validation studies will greatly contribute to our understanding of the human connectome as they improve the framework for the interpretation of the unique insights which can be achieved with diffusion MR techniques.