Abstract
It is generally believed that tuning properties to stimulus orientation (orientation selectivity) emerges first at the primary visual cortex (V1). In the present study, we recorded neurons of the lateral geniculate nucleus (LGN) of anesthetized cat and found that more than 90% of LGN neurons exhibited significant orientation selectivity under stimulus condition with higher spatial frequency and larger size than the optimal. From our experimental results, the receptive fields of LGN neurons are suggested to be elongated along the axis parallel to their preferred orientation. Mean aspect ratio of elliptical receptive field of most LGN neurons is more than 1.5. Additionally, we measured the area-summation curves of neuronal responses with gratings of optimal and orthogonal to the optimal (null) orientations, and found that the degree of surround suppression in LGN was significantly stronger at null orientation than at optimal orientation. This result suggests that orientation-tuned surround suppression enhances orientation tuning of LGN neurons under large stimulus condition. With a presence of surround suppression, orientation-tuning property already appears at the level of LGN, which could be an origin of cortical orientation selectivity in cat. [J Physiol Sci. 2007;57 Suppl:S107]
