Retina horizontal cells



Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the retina.

There are three basic types, named HI, HII and HIII and all three are multipolar cells. The HI cells connect M cones with L cones and are promiscuous, meaning that they do not discriminate which M or L cone they connect with. They do not connect with S cones; that's HII's job, where it connects S with L and M.

They span across cones and summate inputs from them all to control the amount of GABA released back onto the photoreceptors, which hyperpolarises them. Their arrangement together with the on-centre and off-centre bipolar cells that receive input from the photoreceptors constitutes a form of lateral inhibition, increasing spatial resolution at the expense of some information on absolute intensity. The eye is thus more sensitive to contrast and differences in intensity.