title: Virtual dissection and comparative connectivity of the superior longitudinal fasciculus in chimpanzees and humans.
abstract: Many of the behavioral capacities that distinguish humans from other primates rely on fronto-parietal circuits. The superior longitudinal fasciculus (SLF) is the primary white matter tract connecting lateral frontal with lateral parietal regions; it is distinct from the arcuate fasciculus, which interconnects the frontal and temporal lobes. Here we report a direct, quantitative comparison of SLF connectivity using virtual in vivo dissection of the SLF in chimpanzees and humans. SLF I, the superior-most branch of the SLF, showed similar patterns of connectivity between humans and chimpanzees, and was proportionally volumetrically larger in chimpanzees. SLF II, the middle branch, and SLF III, the inferior-most branch, showed species differences in frontal connectivity. In humans, SLF II showed greater connectivity with dorsolateral prefrontal cortex, whereas in chimps SLF II showed greater connectivity with the inferior frontal gyrus. SLF III was right-lateralized and proportionally volumetrically larger in humans, and human SLF III showed relatively reduced connectivity with dorsal premotor cortex and greater extension into the anterior inferior frontal gyrus, especially in the right hemisphere. These results have implications for the evolution of fronto-parietal functions including spatial attention to observed actions, social learning, and tool use, and are in line with previous research suggesting a unique role for the right anterior inferior frontal gyrus in the evolution of human fronto-parietal network architecture.
authors.affiliation: Department of Anthropology, Emory University, 1557 Dickey Drive, Rm 114, Atlanta, GA 30322, USA. Electronic address: ehecht@emory.edu.
authors.forename: Erin E
authors.initials: EE
authors.lastname: Hecht
authors.affiliation: Department of Biomedical Informatics, Emory University School of Medicine, 36 Eagle Row, PAIS Building, 5th Floor South, Atlanta, GA 30322, USA. Electronic address: dgutman@emory.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Gutman
authors.affiliation: Department of Archaeology, University of Exeter, Laver Building, North Park Road, Exeter EX4 4QE, UK. Electronic address: B.A.Bradley@exeter.ac.uk.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Bradley
authors.affiliation: Yerkes National Primate Research Center, Div. Neuropharmacology & Neurologic Diseases & Center for Translational Social Neuroscience, Emory University, 954 Gatewood Rd., Atlanta, GA 30329, USA. Electronic address: tpreuss@emory.edu.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Preuss
authors.affiliation: Department of Anthropology, Emory University, 1557 Dickey Drive, Rm 114, Atlanta, GA 30322, USA. Electronic address: dwstout@emory.edu.
authors.forename: Dietrich
authors.initials: D
authors.lastname: Stout
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D004210:Dissection / Q000379:methods; D005260:Female; D005625:Frontal Lobe / Q000033:anatomy & histology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009434:Neural Pathways / Q000033:anatomy & histology; D002679:Pan troglodytes / Q000033:anatomy & histology*; D010296:Parietal Lobe / Q000033:anatomy & histology*; D066127:White Matter / Q000033:anatomy & histology*
keywords: Cerebral asymmetry; Diffusion tensor imaging; Evolution; Laterality; Tractography; White matter