Two different types of Y cells in the cat lateral geniculate nucleus

The Y pathway in the cat visual system is traditionally viewed as a single channel that originates in the retina. However, most Y cells from the contralateral retina diverge to innervate two different layers of the lateral geniculate nucleus, suggesting a possible channel split: Y_C (Y geniculate cell in layer C) and Y_A (Y geniculate cell in layer A). We tested the functional significance of this anatomical divergence by comparing the response properties of simultaneously recorded Y_C and Y_A geniculate cells with overlapping receptive fields. Our results demonstrate that Y_C and Y_A cells significantly differ in a large number of temporal and spatial parameters including response latency, response transiency, receptive-field size, and linearity of spatial summation. Furthermore, for some of these parameters, the differences between Y _C and Y_A cells are as pronounced as the differences between Y and X cells in layer A. These results along with results from previous studies strongly suggest that Y retinal afferents diverge into two separate channels at the level of the thalamus.