Receptive field mechanisms of sustained and transient retinal ganglion cells in the cat.

Receptive field organization of 135 sustained and 45 transient retinal ganglion cells was investigated in lightly pentobarbitone-anaesthetised cats. Stimuli were concentric annuli presented alone or simultaneously with a small spot centred on the receptive field, against photopic, mesopic or scotopic backgrounds. The addition of the test spot led to reduction in diameter of the centre-surround boundary of receptive fields of sustained retinal ganglion cells (assessed with annuli), and a decrease in diameter of the annulus which was most effective on the surround. In transient cells there was only marginal reduction in diameter of the centre-surround boundary, measured with annuli, and little or no decrease in diameter of the most effective annulus. Reducing background intensity from photopic to scotopic induced changes in response patterns and receptive field organization of sustained and transient retinal ganglion cells which were independent of stimulus intensity. Against photopic backgrounds, large annuli evoked surround-type responses from the majority of transient ganglion cells and from all sustained cells. In the scotopic range, surround-type responses could still be evoked from sustained cells, whereas predominantly centre-type responses were obtained throughout the receptive fields of transient cells. With transition from cone to rod vision, receptive field surrounds of sustained and transient cells became progressively less responsive than centres; in consequence the diameter of the centre-surround boundary increased. The initial, high frequency burst of impulses in discharges at annulus onset or offset became less evident and response latency increased substantially. The results are consistent with a model in which the centre and surround receptive field mechanisms are spatially co-extensive in transient retinal ganglion cells, albeit of different shape, but only partially overlapping in sustained retinal ganglion cells. It is suggested that the surround mechanism in sustained cells is spatially more extensive than the centre mechanism but does not extend entirely through the centre of the field.