Spatial tuning of cells in and around lateral geniculate nucleus of the cat: X and Y relay cells and perigeniculate interneurons

The spatial tuning of X and Y relay cells in the cat lateral geniculate nucleus (LGN), and the spatial tuning of perigeniculate interneurons were investigated with sinusoidal grating patterns, either drifting or undergoing contrast reversal. The responses of geniculate relay cells were analyzed into fundamental and second harmonic components of the stimulus modulation frequency (or drift rate). The spatial tuning of each harmonic component was analyzed separately in terms of Rodieck's two-mechanism model. The spatial parameters for the fundamental response of X-cells and the second harmonic responses of Y-cells were similar. The spatial parameters for the fundamental response of Y-cells were quite different. The spatial tuning of LGN relay cells and their s potentials, presumptive extracellularly recorded synaptic potentials that reflect the retinal input to the LGN cells, were very similar. This implies that there is only a small amount of spatial reorganization of the retinal input in the LGN. The visual responses of perigeniculate interneurons were variable. In some cases there was a significant fundamental response to drifting gratings of high spatial frequency, which implies that the interneurons must receive some X input. In most cases there was an elevation of the discharge rate in response to drifting gratings and second harmonic responses to contrast reversal of gratings or modulation of single bars in the receptive field of the interneuron.