The first synapse in vision: Transmission and modulation

When light enters the eye, a visual image is focussed on a structure at the back of the eye that we call the retina. This structure contains several layers and is connected to the brain via a bundle of fibres we call the optic nerve. However, the brain does not simply receive the raw retinal image. The incoming visual information is first heavily processed by the various layers of the retina. The cells that first detect the light are called photoreceptors. There are two types: cones, which are highly concentrated in the fovea for detail and mainly function during the day, and rods that primarily function in very dark conditions because they are extremely sensitive. Incredibly, substantial processing is already taking place at the point where these cones communicate with two cell types in the next layer, which are known as horizontal cells and bipolar cells. The point at which two cells communicate is called a synapse and so we refer to this as the first retinal synapse. The mechanisms underlying the processing at the first retinal synapse form the topic of this thesis.