Spatial asymmetries in cat retinal ganglion cell responses.
Enroth-Cugell and Robson (1966) first proposed a classification of retinal ganglion cells into X cells, which exhibit approximate linear spatial summation and largely sustained responses, and Y cells, which exhibit nonlinearities and transient responses. Gaudiano (1992a, 1992b, 1994) has suggested that the dominant characteristics of both X and Y cells can be simulated with a single model simply by changing receptive field profiles to match those of the anatomical counterparts of X and Y cells. He also proposed that a significant component of the spatial nonlinearities observed in Y (and sometimes X) cells can result from photoreceptor nonlinearities coupled with push-pull bipolar connections. Specifically, an asymmetry was predicted in the ganglion cell response to rectangular gratings presented at different locations in the receptive field under two conditions: introduction/withdrawal (on-off) or contrast reversal. When measuring the response to these patterns as a function of spatial phase, the standard difference-of-Gaussians model predicts symmetrical responses about the receptive field center, while the push-pull model predicts slight but significant asymmetry in the on-off case only. To test this hypothesis, we have recorded ganglion cell responses from the optic tract fibers of anesthetized cat. The mean and standard deviations of responses to on-off and contrast-reversed patterns were compared. We found that all but one of the cells that yielded statistically significant data confirmed the hypothesis. These results largely support the theoretical prediction.
Gaudiano
P
P
Department of Cognitive and Neural Systems, Boston University, MA 02215, USA.
Przybyszewski
A W
AW
van Wezel
R J
RJ
van de Grind
W A
WA
D000818:Animals; D002415:Cats; D005074:Evoked Potentials, Visual; D005556:Form Perception / Q000502:physiology*; D008959:Models, Neurological; D010775:Photic Stimulation; D012160:Retina / Q000648:ultrastructure; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000145:classification / Q000502:physiology*