Linear mechanism of orientation tuning in the retina and lateral geniculate nucleus of the cat.

1. The orientation tuning of lateral geniculate nucleus (LGN) neurons and retinal ganglion cells (recorded as S potentials in the LGN) was investigated with drifting grating stimuli. 2. Results were compared with a quantitative model, in which receptive fields were constructed from linear, elliptical Gaussian center and surround subunits, and responses could be predicted to gratings of any spatial frequency at any orientation. 3. The orientation tuning of X and Y retinal ganglion cells and LGN neurons was shown to result from the linear mechanism of receptive-field elongation, as data from these cells could be well fit with this model. 4. The responses of LGN neurons and their input retinal ganglion cells were compared. The orientation tuning of LGN neurons was found to be a reflection of the tuning of their retinal inputs, showing that neither intrageniculate neural interactions nor the corticogeniculate projection play any role in LGN orientation selectivity.