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February 1980

Small-Diameter Nonmyelinated Axons in the Primate Corpus Callosum

Author Affiliations

From the Department of Psychology, University of Connecticut, Storrs, and the Department of Neurology, Harvard Medical School, Boston (Dr Swadlow); the Department of Neurology, Stanford (Calif) University Medical School, and the Veterans Administration Hospital, Palo Alto (Dr Waxman); and the Department of Neurology, Harvard Medical School, and Beth Israel Hospital, Boston (Dr Geschwind).

Arch Neurol. 1980;37(2):114-115. doi:10.1001/archneur.1980.00500510072016

• The splenium of the corpus callosum of a primate (Macaca mulatta), examined with the electron microscope, was found to contain both myelinated and nonmyelinated axons. The majority of nonmyelinated axons had diameters of less than 0.25 μ. On the basis of this diameter distribution, it is expected that many callosal axons conduct impulses at velocities of less than 1 m/s and that interhemispheric conduction times for some callosal axons are at least 30 ms and possibly much longer.