1Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 2Fishberg Department of Neuroscience and Friedman Brain Institute, Mt. Sinai School of Medicine, 3Neuroscience Institute, Georgia State University, 4Department of Anthropology, Kent State University, 5Mountain Gorilla Veterinary Program, School of Veterinary Medicine, University of California Davis, 6Rwanda Development Board, Department of Tourism and Conservation, 7Department of Life Sciences, Forensic Sciences Center, University of Coimbra, 8Institute of Neuroscience and Medicine, Research Center Jülich, 9C. and O. Vogt Institute of Brain Research, Heinrich Heine University
Thursday All day, Clinch Concourse
In primates, the Sylvian fissure lies on the lateral side of each cerebral hemisphere, separating the temporal lobe from the frontoparietal operculum. In this study we describe an atypical feature of the neuroanatomy in this region that is selectively present in a minority of primate species. We have observed fusion of the posterior temporal and parietal cortices present in most Eastern gorillas, but rarely in other primates. This fusion occurs between the temporal lobe (often including Heschl’s gyrus in great apes) and the posterior dorsal insula, such that a portion of insular cortex is isolated from the Sylvian fissure.
We examined magnetic resonance images and Nissl-stained and immunolabeled (for parvalbumin, calbindin, neurofilament proteins, and VGluT2) histological sections from 26 primate genera. A fusion between temporal cortex and posterior insula was observed in most Eastern gorilla (Gorilla beringei beringei and G. beringei graueri) specimens, but rarely in other great apes. Four monkey genera (Aotus, Alouatta, Callicebus, and Saguinus) and six strepsirrhines (Avahi, Eulemur, Indri, Loris, Otolemur, and Varecia) showed occasional temporal-insular fusion. Fusions were categorized by hemisphere and were found bilaterally in almost all Eastern gorilla specimens, but were equally likely to be bilateral or unilateral without directional bias in other species.
We suggest that this fusion between auditory and somatosensory cortex is an example of a rare and randomly distributed neuroanatomical feature that has become common in Eastern gorillas, likely through a bottleneck effect. Characterizing the phylogenetic distribution of this morphology highlights a derived feature of these great apes.