Robert Miller
Department of Anatomy and Structural Biology, Otago University

Axonal conduction time and human cerebral laterality

Tuesday 03rd of April 2007 at 12:30pm
3105 Tolman Hall (Beach Room)

The idea of asymmetry of cerebral functions is well established, and depends mainly on psychological evidence. Hitherto there have been few ideas proposed to explain this evidence in terms of lower-level postulates, e.g. about differences between hemispheres in cellular poperties or biochemistry. In 1996 I published a book ("Axonal conduction time and human cerebral laterality",[Gordon and Breach]). The "central hypothesis" of this work is that cortico-cortical axons connecting different parts of the right hemisphere are relatively rapidly conducting, while those in the left hemisphere are on average slower conducting, constituting a "repertoire of delay lines". This talk is based on the 1996 book, but brings the story up to date. It starts with empirical evidence about conduction times in cortico-cortical axons in animals, and then shows how the central hypothesis explains various psychological findings (asymmetry in perception, motor control, vigilance), evidence of directional asymmetry in conduction time between hemispheres, as well as evidence of morphological asymmetry. Lastly, I mention one area of function (some aspects of the representation of speech sounds), where the original hypothesis requires modification, and the difference between right and left in axon properties seems to be the reverse of that originally proposed. Evidence based on diffusion tensor imaging suggests that, while the reasoning in the 1996 book still holds, the pattern of asymmetry of axonal properties is probably more complex than originally proposed.

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