COMPARISON OF RECEPTIVE-FIELD PROPERTIES OF X AND Y GANGLION-CELLS WITH X AND Y LATERAL GENICULATE CELLS IN THE CAT

1. To examine the transmission of visual information through the lateral geniculate nucleus, we have studied the receptive-field properties of 65 X and Y optic tract axons and compared them with the receptive-field properties of X and Y LGN cells in paralyzed cats anesthetized with N2O/O2 (70/30%). The same experimental conditions and quantitative methods have been used as in the preceding study of LGN cells (2). 2. The spatiotemporal organization of the receptive fields of X and Y retinal axons are similar to those of X and Y LGN cells. X ganglion cell receptive fields show a simple center-surround organization, whereas Y ganglion cell receptive fields show a more complex organization with three concentric regions: a central region of center-type response, a region of mixed center-type and surround-type responses, and a region of surround-type response. 3. The inhibitory strengh of the surrounding region was tested with a centrally located flashing light spot of successively increased diameter. As in the LGN, the inhibitory strenght of the surrounding region was stronger in retinal X-cells than in retinal Y-cells, and the strength of the inhibition decreased as the diameter of the receptive-field center increased. 4. The decrease of the inhibitory strength of the surrounding region with increasing distance from the receptive-field center was similar in the retina and in the LGN for cells belonging to the same class (X or Y) and having the same receptive-field center size. 5. The differences in properties in the LGN between small-field X-, large-field X-, and Y-cells are best explained by assuming that they are driven, respectively, by small-field X, large-field X, and Y retinal ganglion cells. There does not appear to be a significant mixing of properties either between cells having different receptive-field center sizes. 6. The principal transformation we found between retinal and LGN units is that X LGN cells have sharply lower spontaneous activities and driven activities, as compared with X ganglion cells. Y LGN units show only a small decrease in spontaneous activity in comparison with Y ganglion cells. 7. We conclude that there is a significant alteration in the LGN only in the properties of X-cells, possibly by way of a strong inhibitory pool converging on X LGN units. We further suggest that this inhibitory pool plays a role in the modulation of transmission of information through the LGN only in the X channel, while the Y channel appears to be relatively unaffected.