Regional and Directional Differences in the Lateral Spread of Retinal Potentials in the Octopus

Abstract

RECENTLY the visual system of the octopus has been investigated by several anatomical and behavioural methods. From behavioural investigations of pattern discrimination, Sutherland¹ has proposed a theory of vertical and horizontal coding of pattern information. The anatomical complexity required for such neural coding is certainly present in the optic lobes. However, Young² has described axon collaterals between adjacent receptor cells within the retina and has suggested the possibility of synaptic influence on the spatial relations of the information propagated from the retina. Previous work in this laboratory has disclosed that there are two responses to light stimulation in the retina of the octopus: a sustained negative response on the vitreal surface and a sustained positive response in the deeper layer³. The two responses behave differently with respect to stimulus variables, and thus appear to reflect two potential origins rather than a single sink-source generator⁴. The deep, positive, response has been suggested as arising, at least partially, from the receptor cells. In the work reported here, it was found that for the deep response there is a spread of positivity toward the centre of the retina and a spread of negativity toward the periphery; this might represent a function of the lateral connexions described anatomically².