Contrast Adaptation in the Lateral Eye of \u3ci\u3eLimulus polyphemus\u3c/i\u3e

Luminance and contrast adaptation are neuronal mechanisms that the retina applies for continuous adjustment to light sensitivity though a collection of cellular and synaptic mechanisms distributed across the retinal network, thus accommodating the wide input range of the visual system within the constricted output range of retinal ganglion cells. Luminance mean adaptation has been demonstrated in the output neurons of the invertebrate eye (eccentric cells), and the aim of the study was to investigate whether the homology in visual processing extends to luminance variance (contrast) adaptation as well. The spike trains of individual eccentric cells were recorded from live horseshoe crabs to white noise stimuli of varying contrast delivered to optically-isolated ommatidial receptors. Linear-nonlinear models estimated from the spike output of eccentric cells decreased in gain with increasing contrast of white noise, suggesting an unknown mechanism of contrast adaptation may operate in the retina. Given the simple organization of the horseshoe crab eye determining whether this mechanism exists in the retina is of fundamental importance to vision research