Seeing with S cones.
The S cone is highly conserved across mammalian species, sampling the retinal image with less spatial frequency than other cone photoreceptors. In human and monkey retina, the S cone represents typically 5-10% of the cone mosaic and distributes in a quasi-regular fashion over most of the retina. In the fovea, the S cone mosaic recedes from a central "S-free" zone whose size depends on the optics of the eye for a particular primate species: the smaller the eye, the less extreme the blurring of short wavelengths, and the smaller the zone. In the human retina, the density of the S mosaic predicts well the spatial acuity for S-isolating targets across the retina. This acuity is likely supported by a bistratified retinal ganglion cell whose spatial density is about that of the S cone. The dendrites of this cell collect a depolarizing signal from S cones that opposes a summed signal from M and L cones. The source of this depolarizing signal is a specialized circuit that begins with expression of the L-AP4 or mGluR6 glutamate receptor at the S cone-->bipolar cell synapse. The pre-synaptic circuitry of this bistratified ganglion cell is consistent with its S-ON/(M+L)-OFF physiological receptive field and with a role for the ganglion cell in blue/yellow color discrimination. The S cone also provides synapses to other types of retinal circuit that may underlie a contribution to the cortical areas involved with motion discrimination.
Calkins
D J
DJ
Departments of Ophthalmology, Neurobiology and Anatomy, and Neurology and the Center for Visual Science, University of Rochester Medical Center, Rochester, NY 14642, USA.
D000818:Animals; D003118:Color Perception / Q000502:physiology*; D006801:Humans; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D017299:Rod Opsins / Q000378:metabolism; D014792:Visual Acuity / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology
D017299:Rod Opsins