Gross anatomical tractography (GAT) proposed a change from the 'Two laminae concept' to the 'Neuronal unit concept' on the structure of the human hippocampus.

The three dimensional structure of the human hippocampus was studied using the gross anatomical tractography (GAT) of Klingler technique. Eight hippocampi were obtained from seven donors to the Kanazawa Medical University, fixed in 5% formaldehyde, frozen and thawed twice, then dissected both by naked eye and under a dissecting microscope.The subiculum was segmented into 7-12 hillocks along the antero-posterior axis. The hillocks were organized with the white matter process and its gray matter covering. Cornu ammonis 3 (CA3) was represented by gray matter located in a longitudinal trough about 1 mm wide between the base of the fimbria and fiber bundles of the stratum lacunosum. CA3 was traversed and segmented by numerous short fiber fasciculi extending from the dentes of the margo denticulatus. The stratum radiatum, lacunosum and moleculare were differentially dissected. They not only contained systematically arranged neuronal fibers but also frameworks to allow passage of blood vessels. The polymorphic layer (PL) consisted of many italic L-shaped bars that were segmented, fused side-by-side and arrayed along the antero-posterior axis. The stratum granulosum (SG) lined the superior surface of PL as square plates and inferior surface of PL as thin folds. Thus, the SG was also segmented, although a little arbitrarily. CA4 was found not to be a neuronal plate, but instead comprised numerous neuronal rods that were segmentally arranged in accord with segmentation of CA3.On the basis of these segmentations, we conclude that, structurally, the human hippocampus is an antero-posterior succession of neuronal units, each consisting of the subicular hillock, dens, CA3, granular cell plates and folds, PL bars and CA4 rods.