From the Beginning
In 1933, G. H. Bishop published a report entitled “Fibre Groups in the Optic Nerve.” This is perhaps the earliest study, morphological or physiological, to which present concepts of the parallel organization of the visual pathways can be traced. It was an electrophysiological study in which Bishop obtained oscillographic records of compound action potentials, generated in the excised optic nerve of the frog, and in the exposed but still-attached nerve of the rabbit, by a brief electrical shock applied to the nerve some distance from the recording lead. In both species, the compound action potential showed early and later components (Fig. 1.1), suggesting that the axons of the nerve were not homogeneous in the velocity at which they conduct action potentials, but rather fell into two or more groups (Bishop suggested three), with distinct conduction velocities and therefore distinct calibers. In the frog, the three groups had conduction velocities of 10, 3 and 0.4 m/sec; in the rabbit, the approximate values were 20–50, 7–17, and 4 m/sec. The report concluded with an optimistic prediction that the presence of conduction velocity groupings in the optic nerve would be a useful starting point for the further investigation of the visual pathways.
KeywordsOptic Nerve Ganglion Cell Receptive Field Conduction Velocity Retinal Ganglion Cell
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