Binocular interaction in the perigeniculate nucleus of the cat.

We have recorded from single cells in the perigeniculate nucleus (PGN) of the cat to determine their response properties. Quantitative tests have been conducted with sinusoidal gratings. Using optimal stimulus parameters, determined monocularly, we explored binocular interaction by varying the relative phase between dichoptically presented gratings. Monocularly, cells exhibit varying degrees of response specificities with respect to stimulus orientation and spatial frequency. Binocularly, we have identified six types of response. The most prominent, type 1, found for half the cells, is phase-specific binocular interaction at the fundamental frequency component of the drifting grating. For these cells, mean response rate is independent of interocular phase. The remaining types of binocular responses involve varying degrees of interaction at different harmonic components. For a quarter of the sample, no binocular interaction was observed. To investigate the role of cortical input to PGN, visual cortex was removed from some cats. Subsequent study of PGN cells indicated that response properties were generally similar to those found in intact animals. We conclude that PGN response properties are determined primarily by subcortical inputs.