Chromatic, adaptive, and general properties of cat retinal ganglion and lateral geniculate cells: a mid-mesopic study

Abstract

Data were collected at the retinal ganglion (RGC) and lateral geniculate cell (LGC) levels in lightly anaesthetised cats at a mid- mesopic background adapting luminance. Investigation of the rod- and cone-mediated properties of cells was accomplished by differentially influencing the rod and cone mechanisms with narrow-band light at short (452 nm) and long (578 nm) wavelengths respectively.
For RGCs, area ratios of rod-mediated to cone-mediated receptive field centres (RFCs) ranged from 0.6:1 to 2.9:1, with 66% of cells having larger rod than cone centres. RFCs were elliptical, the magnitude of ellipticity being similar for rod and cone centres and in agreement with values given by Hammond (1974). Almost 60% of maps had their major axis orientated within ±20° of horizontal, confirming the results of Hammond (1974). In addition, 69% exhibited non-concentric rod and cone centre maps and 24% displayed two spatially separate regions of maximal sensitivity* possibly one for cones and the other for rods. The adaptive state, assessed by the technique of Hammond and James (1971) and based upon that of Barlow and Levick (1968), was found to vary over a 0.6 log. units range. However, in contrast to the results and predictions of Enroth-Cugell and Shapley (1973b) its value was not correlated with the visual field location of the receptive field or with RFC area. Moreover, the mean value of the adaptive state did not differ between brisk sustained and transient cells, despite their dissimilar RFC sizes.
For LGCs, the rod- to cone-centre area ratios ranged from equality to 1.4:1, with 35% having larger rod than cone centres. 68% of maps had horizontally oriented major axes. The calculated mean ellipticity ratios were similar for rod and cone centres, and comparable to the retinal data.