TYPES OF VISUAL RESPONSE FROM SINGLE UNITS IN THE OPTIC TECTUM AND OPTIC NERVE OF THE GOLDFISH.

Abstract

Using metal‐filled micropipette electrodes we have recorded responses from single units in the optic tectum and optic chiasma of the goldfish. Responses were evoked by visual stimulation with spots of light and with black discs of various sizes. In many cases, after recording from a unit, the position of the electrode tip was marked by making an electrolytic lesion 10‐50 µ in diameter. These lesions were all found to be in one of the fibre layers of the tectum, either in one of the three most superficial fibre layers which contain the optic afferent fibres, or in the deepest layer of fibres. The two most superficial fibre layers contained “on”, “off” and brief “on‐off” units whch did not appear to be segregated into strata containing only one type of unit. Some of these units were directionally sensitive. Slowly‐adapting “on” and “off” units predominated in the third fibre layer. The deepest fibre layer, below the main layer of tectal cells, contained all the types of units found in the fibre layers near the surface of the tectum. All the types of response found in the optic tectum were also recorded from the optic chiasma. Maps were made of the receptive fields of units recorded in the optic chiasma and at various depths in the optic tectum. Receptive fields organized into adjacent, rather than concentric “on” and “off” zones, were frequently found in the optic chiasma and at all levels in the tectum. The topographical projection of the visual field onto the optic tectum was mapped. Units encountered during an electrode penetration into the tectum normal to its surface were found to have overlapping receptive fields. No ipsilateral projection was found.