title: The diameter of cortical axons depends both on the area of origin and target.
abstract: In primates, different cortical areas send axons of different diameters into comparable tracts, notably the corpus callosum (Tomasi S, Caminiti R, Innocenti GM. 2012. Areal differences in diameter and length of corticofugal projections. Cereb Cortex. 22:1463-1472). We now explored if an area also sends axons of different diameters to different targets. We find that the parietal area PEc sends thicker axons to area 4 and 6, and thinner ones to the cingulate region (area 24). Areas 4 and 9, each sends axons of different diameters to the nucleus caudatus, to different levels of the internal capsule, and to the thalamus. The internal capsule receives the thickest axon, followed by thalamus and nucleus caudatus. The 2 areas (4 and 9) differ in the diameter and length of axons to corresponding targets. We calculated how diameter determines conduction velocity of the axons and together with pathway length determines transmission delays between different brain sites. We propose that projections from and within the cerebral cortex consist of a complex system of lines of communication with different geometrical and time computing properties.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden giorgio.innocenti@ki.se.
authors.forename: Giorgio M
authors.initials: GM
authors.lastname: Innocenti
authors.affiliation: Neuroscience Institute Cavalieri Ottolenghi (NICO), Department of Neuroscience, University of Turin, Turin, Italy and.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vercelli
authors.affiliation: Department of Physiology and Pharmacology, University of Rome Sapienza, Rome, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Caminiti
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D001710:Biotin / Q000031:analogs & derivatives; D001921:Brain / Q000166:cytology* / Q000502:physiology; D003911:Dextrans; D008251:Macaca; D008854:Microscopy, Electron; D008959:Models, Neurological; D009431:Neural Conduction; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D056347:Neuroanatomical Tract-Tracing Techniques; D010784:Photomicrography
chemical_list: D003911:Dextrans; C076397:biotinylated dextran amine; D001710:Biotin
keywords: conduction velocity; cortical area; internal capsule; nucleus caudatus; thalamus