title: Contrast invariance of orientation tuning in the lateral geniculate nucleus of the feline visual system.
abstract: Responses of most neurons in the primary visual cortex of mammals are markedly selective for stimulus orientation and their orientation tuning does not vary with changes in stimulus contrast. The basis of such contrast invariance of orientation tuning has been shown to be the higher variability in the response for low-contrast stimuli. Neurons in the lateral geniculate nucleus (LGN), which provides the major visual input to the cortex, have also been shown to have higher variability in their response to low-contrast stimuli. Parallel studies have also long established mild degrees of orientation selectivity in LGN and retinal cells. In our study, we show that contrast invariance of orientation tuning is already present in the LGN. In addition, we show that the variability of spike responses of LGN neurons increases at lower stimulus contrasts, especially for non-preferred orientations. We suggest that such contrast- and orientation-sensitive variability not only explains the contrast invariance observed in the LGN but can also underlie the contrast-invariant orientation tuning seen at the level of the primary visual cortex.
authors.affiliation: Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Vic, 3010, Australia.
authors.forename: Sivaram
authors.initials: S
authors.lastname: Viswanathan
authors.affiliation: Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Vic, 3010, Australia.
authors.forename: Jaikishan
authors.identifier: http://orcid.org/0000-0001-8925-723X
authors.initials: J
authors.lastname: Jayakumar
authors.affiliation: Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Vic, 3010, Australia.
authors.forename: Trichur R
authors.initials: TR
authors.lastname: Vidyasagar
mesh_terms: D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity / Q000502:physiology*; D005829:Geniculate Bodies / Q000502:physiology*; D009433:Neural Inhibition; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation; D014795:Visual Pathways / Q000502:physiology
keywords: lateral geniculate nucleus; orientation selectivity; single cell electrophysiology; visual cortex