Postmortem Dissections of the Papez Circuit and Nonmotor Targets for Functional Neurosurgery

Abstract

The Papez circuit was first described as the anatomic basis of emotion. Subsequent studies consolidated recognition of its limbic activities but showed a more important role in memory. Anatomic dissections and advanced neuroimaging have deepened our understanding of the various interconnections and white matter tracts present in this circuit. The aim of our study is to describe the anatomy of the Papez circuit through cadaveric dissection with correlation to ultrahigh-field magnetic resonance imaging (MRI) and MRI tractography. White fiber dissection was performed on 5 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 ultrahigh resolution, 7T structural MRI, and 17.6T diffusion tractography to further show the anatomy. 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 ultrahigh-field structural and diffusion MRI. We showed for the first time (through portmortem dissection) fibers directly connecting the anterior thalamic nucleus and the subgenual cingulate via the septal area. 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 showing new areas of connectivity with adjacent structures and possibilities for surgical approaches or stimulation.