Efferent axons in the fish optic nerve and their effect on the retinal ganglion cells

Recordings were taken from small bundles of axons dissected away from the otherwise intact optic nerve of the trigger fish, Hemibalistes chrysopterus. Proximal nerve stumps showed unitary activity of efferent axons which are activated by visual, vestibular, vibratory and tactile stimuli. Distal stumps showed predominantly the discharges of retinal ganglion cells which have a sustained response in either the light or dark and which are inhibited by the opposite condition. These retinal ganglion cells are also excited by vestibular, vibratory and tactile stimuli provided the optic nerve is almost intact. It is inferred that the excitation of the retinal ganglion cells by non-visual stimuli is effected by the centrifugal fibres mentioned above. Ablation of various lobes of the brain shows that the efferent fibres continue to respond after ablation of the frontal lobes and the cerebellum. The response is weakened by the ablation of the ipsilateral optic tectum and abolished when the contralateral tectum is removed.