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

Three-dimensional anatomical structure formed by granule cell layer and pyramidal cell layer in human hippocampus

In the human hippocampus, the pyramidal layer consists of the inferior aspect of the hippocampus which is organized segmentally. Each segment, together with granule layer of the dentate gyrus, exhibits structural unity. In humans, ellipsoidal protrusions called pyramidal hillocks (PHs), which consist of a thick pyramidal cell layer (PL), are present in the inferior aspect of the hippocampus, and are segmentally organized along a longitudinal axis. It is also known that the granule cell layer (GL) of the dentate gyrus (DG) is not a smooth but undulated structure. However, the cytoarchitectural relationships between the protrusions and undulation have yet to be studied well. Here, we aimed to clarify the three-dimensional cytoarchitecture of the PL and GL of human hippocampus. For that purpose, the GL and PL were three-dimensionally reconstructed from serial sections of human hippocampus stained with hematoxylin and eosin. The GL was shaped as tubing with an opening in the dorsal part, and undulated especially in the medial part, forming digit-like processes. In the base of a digit-like process, protrusions of the GL extended laterally, with longer ones reaching the lateral edge, whereas shorter ones disappeared around the medial 1/3 of the GL. Consequently, the lateral part of the GL was undulated loosely. In the ventral view of the PL, the ellipsoidal PHs were sagittally aligned, whereas in the top view, each PH formed an ellipsoidal trough. Each structural unit was formed by a trough of the PH along the bottom, and had a longer GL protrusion in the upper-center, and shorter GL protrusions located between the longer protrusions and the lateral edge of the GL. A digit-like process extended into a dens. It is concluded that a unit of the PH and the GL comprises the longitudinal segmental formation of the hippocampus.

A Comprehensive Review of Medical Imaging Equipment Used in Cadaveric Studies

Medical imaging techniques have led to great advances in clinical anatomy and forensic pathology. New and emerging technologies allow healthcare professionals to view and understand the human body from different perspectives. This gives way to new and improved interventions, treatment plans, and an overall understanding of the human body. Herein, we present a comprehensive review of the various medical imaging equipment used in cadaveric studies along with their individual strengths and limitations.

Direct Visualization and Mapping of the Spatial Course of Fiber Tracts at Microscopic Resolution in the Human Hippocampus

While hippocampal connectivity is essential to normal memory function, our knowledge of human hippocampal circuitry is largely inferred from animal studies. Using polarized light microscopy at 1.3 µm resolution, we have directly visualized the 3D course of key medial temporal pathways in 3 ex vivo human hemispheres and 2 ex vivo vervet monkey hemispheres. The multiple components of the perforant path system were clearly identified: Superficial sheets of fibers emanating from the entorhinal cortex project to the presubiculum and parasubiculum, intermixed transverse and longitudinal angular bundle fibers perforate the subiculum and then project to the cornu ammonis (CA) fields and dentate molecular layer, and a significant alvear component runs from the angular bundle to the CA fields. From the hilus, mossy fibers localize to regions of high kainate receptor density, and the endfolial pathway, mostly investigated in humans, merges with the Schaffer collaterals. This work defines human hippocampal pathways underlying mnemonic function at an unprecedented resolution.

Ultra-high resolution in-vivo 7.0T structural imaging of the human hippocampus reveals the endfolial pathway

The hippocampus is a very important structure in memory formation and retrieval, as well as in various neurological disorders such as Alzheimer's disease, epilepsy and depression. It is composed of many intricate subregions making it difficult to study the anatomical changes that take place during disease. The hippocampal hilus may have a unique neuroanatomy in humans compared to that in monkeys and rodents, with field CA3h greatly enlarged in humans compared to that in rodents, and a white-matter pathway, called the endfolial pathway, possibly only present in humans. In this study we have used newly developed 7.0T whole brain imaging sequence, balanced steady-state free precession (bSSFP) that can achieve 0.4mm isotropic images to study, in vivo, the anatomy of the hippocampal hilus. A detailed hippocampal subregional segmentation was performed according to anatomic atlases segmenting the following regions: CA4, CA3, CA2, CA1, SRLM (stratum radiatum lacunosum moleculare), alveus, fornix, and subiculum along with its molecular layer. We also segmented a hypointense structure centrally within the hilus that resembled the endfolial pathway. To validate that this hypointense signal represented the endfolial pathway, we acquired 0.1mm isotropic 8-phase cycle bSSFP on an excised specimen, and then sectioned and stained the specimen for myelin using an anti-myelin basic protein antibody (SMI 94). A structure tensor analysis was calculated on the myelin-stained section to show directionality of the underlying fibers. The endfolial pathway was consistently visualized within the hippocampal body in vivo in all subjects. It is a central pathway in the hippocampus, with unknown relevance in neurodegenerative disorders, but now that it can be visualized noninvasively, we can study its function and alterations in neurodegeneration.