We present a quantitative analysis of the visual response properties of single neurons in the dorsal lateral geniculate nucleus (dLGN) of wild-type C57Bl/6J mice. Extracellular recordings were made from single dLGN cells in mice under halothane and nitrous oxide anesthesia. After mapping the receptive fields (RFs) of these cells using reverse correlation of responses to flashed square stimuli, we used sinusoidal gratings to describe their linearity of spatial summation, spatial frequency tuning, temporal frequency tuning, and contrast response characteristics. All cells in our sample had RFs dominated by a single, roughly circular “center” mechanism that responded to either increases (on-center) or decreases (off-center) in stimulus luminance, and almost all cells passed a modified null test for linearity of spatial summation. A difference of Gaussians model was used to relate spatial frequency tuning to the spatial properties of cells' RFs, revealing that mouse dLGN cells have large RFs (center diameter approximately 11°) and correspondingly poor spatial resolution (approximately 0.2c/°). Temporally, most cells in the mouse dLGN respond best to stimuli of approximately 4 Hz. We looked for evidence of parallel processing in the mouse dLGN and found it only in a functional difference between on- and off-center cells: on-center cells were more sensitive to stimulus contrast than their off-center neighbors.
Dynamics of spatial frequency tuning in lateral geniculate nucleus
