Compound action potentials of cat optic nerve produced by stimulation of optic tracts and of optic nerve

Compound action potentials of the optic nerve in cat were studied with electrodes in the optic tracts and in the prechiasmal and retrobulbar portions of the optic nerve. Recordings from either portion of the nerve showed strong electrical stimulation in one or both tracts to be less effective than moderate stimulation through the other electrode in the nerve. Either type of stimulation produced action potentials with discrete electrical components. Number and latency of components varied depending on stimulus parameters and thus did not permit classification of discrete fiber groups. Stronger stimulation of the optic nerve, however, reduced prominence and number of individual components and led to large action potentials with smoother contour which included conduction velocities of 3.5–70 m/sec and a maximum at 15–25 m/sec. These results agree with the anatomy of the optic nerve, particularly with reports on the total range of fiber sizes, on a unimodal distribution of sizes within this range, and on segregation of fiber sizes in different parts of the cross section of optic nerve and tract.