Figure 3.

Pathway-specific DTT in a postmortem common marmoset revealing the course of the corticospinal tract with pyramidal decussation. A, DTT of the CST was conducted by placing the ROI in the pyramid of the medulla and tracing caudally. Note that the volume of traced tracts decrease as the tracing was carried caudally, because many tracts became untraceable because of the partial volume effect. B, By placing secondary ROIs in areas of the upper cervical spinal cord known to contain CST fibers, CST fibers that pass through both ROIs could be depicted. C, Lateral CST fibers that crossed over to and descended the contralateral lateral funiculus in a pattern suggesting pyramidal decussation were depicted in yellow. D, Uncrossed lateral fibers descending the ipsilateral lateral funiculus were depicted in red. E, Lateral fibers descending the ipsilateral anterior funiculus were depicted in blue. The fact that DTT was capable of accurately depicting all three known pathways of the CST is significant. However, it is important to note that the depicted DTT tracts do not accurately reflect the volume of nerve fibers, because it is known that the lateral CST contains the majority of CST fibers. F, G, DTT of the pyramidal decussation superimposed on three-dimensional MR images to macroscopically confirm that the pyramidal decussation was depicted in the proper height in the medulla and the upper cervical cord, using the cerebellum as a reference point. H, DTT of the pyramidal decussation superimposed on axial color-coded FA maps. I, J, Axial histological slices of the same points in H stained for CaMKII-α to reveal the location of CST fibers (I) and LFB to delineate the configuration of the white matter (J). In each slice, the area through which the DTT CST tract passes was positive for CaMKII-α and LFB, confirming the accuracy of DTT.