Postmortem Dissections of the Papez Circuit and Non-Motor Targets for Functional Neurosurgery.

ABSTRACT Background The Papez circuit was first described as the anatomical basis of emotion. Subsequent studies consolidated recognition of its limbic activities but eventually demonstrated a more important role in memory. Anatomical dissections and advanced neuroimaging have deepened our understanding of the various interconnections and white matter tracts present in this circuit. The aim of our paper is to describe the anatomy of the Papez circuit through cadaveric dissection with correlation to ultra-high field MRI and MRI tractography. Methods White fiber dissection was performed on five cadaveric human brain hemispheres. The Papez circuit was dissected mediolaterally to show its anatomy and relation to other nuclei and tracts. Open source MRI tractography data from the Human Connectome Project is combined with ultra-high resolution, 7T structural MRI and 17.6T diffusion tractography to further illustrate the anatomy. Results The network connecting the anterior and posterior cingulate, entorhinal cortex, hippocampus, fimbria, dentate gyrus, fornix, mammillary bodies, and anterior thalamus was described using white matter fiber dissection, and compared with MRI tractography and ultra-high field structural and diffusion MRI. We demonstrated for the first time (through port-mortem dissection) fibers directly connecting the anterior thalamic nucleus and the subgenual cingulate via the septal area. Conclusions The description of the anatomy of the Papez circuit through cadaveric dissection and comparisons with advanced neuroimaging studies allow a better understanding of its three-dimensional spatial layout, in addition to demonstrating new areas of connectivity with adjacent structures, possibilities for surgical approaches or stimulation.