THE RESPONSE OF SINGLE OPTIC NERVE FIBERS OF THE VERTEBRATE EYE TO ILLUMINATION OF THE RETINA

In a series of three papers Adrian and Matthews (1927, 1928) presented a study of the discharge of impulses in the optic nerve of the eel’s eye, and so opened a new approach to problems of visual physiology. In those papers the simultaneous activity of large numbers of optic nerve fibers was recorded. The possibility of extending that work to an analysis of the activity in single optic nerve fibers was suggested by the subsequent investigation of Hartline and Graham (1932) on the optic nerve fibers of a primitive arthropod eye (Limulus). The present paper describes the discharge of impulses in single optic nerve fibers of the cold-blooded vertebrate eye, in response to illumination of the retina. METHOD. The usual methods for obtaining action potentials from only one fiber in a nerve trunk have not succeeded when applied to the vertebrate optic nerve. It is therefore necessary to utilize the intra-ocular portion of the optic nerve fibers, by exposing the fundus of the eye and dissecting small bundles of fibers from the anterior (vitreous) surface of the retina, where they converge to the head of the optic nerve. From a, freshly pithed animal (in most of these experiments large bullfrogs (Rima catesbiana) were used) an eye is excised, pinned fundus down in a moist chamber, and its anterior half (cornea, lens, choroid body) removed. A wide V-shaped cut extending almost to the nerve head gives access to the fundus and permits the vitreous humor to be drained away. It is then possible to dissect free small bundles of nerve fibers for a length of 1 to 2 mm., and these may be further dissected until only one fiber remains active. A bundle is severed where it enters the nerve head and the cut end lifted up onto one of the electrode wicks; the second electrode is diffuse, touching the surface of the retina The action potentials from such bundles of nerve fibers are amplified and recorded by means of an oscillograph. The preparation is mounted in a light-tight, electrically shielded box, in the hollow walls of which water at constant temperature (ca. 20°C.) is circulated.