Postmortem examination of patient H.M.'s brain based on histological sectioning and digital 3D reconstruction

Abstract

Modern scientific knowledge of how memory functions are organized in the human brain originated from the case of Henry G. Molaison (H.M.), an epileptic patient whose amnesia ensued unexpectedly following a bilateral surgical ablation of medial temporal lobe structures, including the hippocampus. The neuroanatomical extent of the 1953 operation could not be assessed definitively during H.M.'s life. Here we describe the results of a procedure designed to reconstruct a microscopic anatomical model of the whole brain and conduct detailed 3D measurements in the medial temporal lobe region. This approach, combined with cellular-level imaging of stained histological slices, demonstrates a significant amount of residual hippocampal tissue with distinctive cytoarchitecture. Our study also reveals diffuse pathology in the deep white matter and a small, circumscribed lesion in the left orbitofrontal cortex. The findings constitute new evidence that may help elucidate the consequences of H.M.'s operation in the context of the brain's overall pathology.

Figure 1. Ventral surface of H.M.’s brain.

The fixed specimen was photographed after removal of the leptomeninges. Evidence of the surgical lesions in the temporal lobes is highlighted by white geometric contours (a, b). A mark produced by the oxidation of one of the surgical clips inserted by Scoville is visible on the parahippocampal gyrus of the right hemisphere (black arrow). (c) encloses a lesion in the orbitofrontal gyrus that affects the cortex and WM. Marked cerebellar atrophy is consistent with H.M.’s long-term treatment with phenytoin. Scale bar, 1 cm.

Figure 2. Anatomical and histological views of the lesion and residual hippocampus.

(a,d,g,j) Cross-sectional anatomy of patient H.M.’s MTL shown at four different levels. The values below the tissue indicate the section number and in parenthesis, the distance from the origin of the standard coordinate system (positive if the level is anterior to the anterior commissure, negative if posterior). Scale bar, 1 cm. (b,c), (e,f), (h,i), (k,l): close-up images acquired from thionin-stained tissue slices; these panels illustrate histological detail for the selection boxes in a, d, g, j, respectively. Scale bar, 5 mm. (m) Horizontal cross-sectional view reconstructed orthogonally from the original coronal images showing the correct alignment of the anterior and posterior commissures. (n–q): normal anatomy and histology of the MTL at the levels shown for the brain of patient H.M. The images were derived from brain slices belonging to a neurologically normal, age-matched individual. Scale bar, 5 mm. PPo, planum polare; MTG, middle temporal gyrus; ITG, inferior temporal gyrus; ITP, inferior temporopolar cortex; PRC, perirhinal cortex; CMA, centromedial amygdala; opt, optic tract; LV, lateral ventricle; PHG, parahippocampal gyrus; Ent, entorhinal cortex; LGN, lateral geniculate nucleus; Hp, hippocampus; FuG, fusiform gyrus; fi, fimbria; SN, substantia nigra; FL, frontal lobe; Cd, caudate; Pu, putamen; I, insula; AC, anterior commissure; Cl, claustrum; TL, temporal lobe; PC, posterior commissure; Ce, cerebellum; OL, occipital lobe; OrG, orbital gyrus; Pir, pirifom cortex; Amg, amygdala. The asterisks delimit the entorhinal cortex.

Figure 3. Sagittal views of the right (a) and left (b) hemispheres reconstructed from the original series of coronal microtome images.

The grey lines intersect at the origin of the origins of the standard coordinate system used for the orientation of the specimen. The blue line indicates the most anterior level of the temporal lobes (the temporal poles, which are damaged are not shown in this image). The orange rectangle represents the bounding box that contains the posterior spared hippocampus (outlined in green), the widest extent of which is at a more medial level than this image shows. The black arrows identify the level at which a surgical clip was positioned on a blood vessel. The red arrows indicate the presence of lesions in the subcortical WM. AC, plane of the anterior commissure; PC, plane of the posterior commissure; AC–PC, ideal plane at the level of both the AC and PC; Ce, cerebellum; LG, lateral geniculate nucleus; Pu, putamen; TP, temporal pole; RH, right hemisphere; LH, left hemisphere. Scale bar, 1 cm.

Figure 4. Triangulated 3D surface reconstruction of H.M.’s spared left hippocampus.

The orange bounding box delimits the dimensions of the structure; different segments indicate different measurements; a: anterior-to-posterior extent in the coronal plane, b (dotted): major diagonal axis, c: anatomical length. The compass cube (A: anterior, L: lateral, S: superior) also functions as scale bar: 5 mm. The insert at the bottom right shows a similarly constructed model from the brain of a neurologically normal subject (78-year-old female donor; volume of the right hippocampus=3.04 mm³; total brain weight 1,278). Ce, cerebellum; FuGR, fusiform gyrus of right hemisphere; IT, inferior temporal gyrus; SN, substantia nigra; Amg, amygdala.

Figure 5. Thionin-stained histological section at the level of the lateral geniculate nuclei.

(a) Whole section. Scale bar, 1 cm. (b,c) Higher-magnification cross-sectional image of the dentate gyrus of the spared hippocampus. The fimbria is visible below the lateral geniculate nucleus. Scale bar, 1 mm. (d,e) × 20 magnification image of neurons in the CA4 region of the hippocampus (in the location of the box). Scale bar, 50 μm. PrG, precentral gyrus; PL, parietal lobe; CG, cingulate gyrus; LV, lateral ventricle; cc, corpus callosum; fx, fornix; Th, thalamus; TL, temporal lobe; LG, lateral geniculate nucleus; RN, red nucleus; SN, substantia nigra; DG, dentate gyrus; fi, fimbria.

Figure 6. Deep WM pathology.

(a,b) Lesions in the deep WM were visible in postmortem T1-weighted MRI images acquired ex situ (scale bar, 1 cm) and were confirmed by myelin silver-impregnation (c) and haematoxylin and eosin (H&E) staining (d). Scale bar, 5 mm.

Figure 7. Lesion in the left frontal lobe.

The reconstructed anatomical volume revealed a small lesion in the lateral orbital gyrus of the left frontal lobe. This is the only lesion affecting the gross structure of the cerebral cortex outside of the MTL. (a) T1-weighted MRI of the fixed brain acquired ex situ before cryo-sectioning. Scale bar, 1 cm. The same lesion is shown in histological material that was stained for myelinated fibres (b) and neuronal cell bodies (c). Scale bar, 1 mm.