Ido Perlman, Helga Kolb and Ralph Nelson Horizontal cells are
the interneurons of distal vertebrate retina. They provide the
pathways for both local and long range interactions between
photoreceptors. These interactions are called feedback signals.
Feedback signals adjust the gain of photoreceptor synaptic
output, both as seen in the horizontal cells themselves and in
the adjacent, proximally projecting bipolar cells. In forming a
distal, lateral synaptic network, horizontal cells enrich not
only their own physiology but that of presynaptic and
postsynaptic partners. They generate spatial opponency in both
cones and bipolar cells. They also generate color opponency in
cones, bipolar cells, and chromatic horizontal-cell subtypes.
The actions of horizontal cells propagate forward in the retina,
can be identified in the physiology of retinal ganglion cells,
and in visual perception. Horizontal cell actions are in turn
tuned by neuromodulators released by other retinal neurons. The
first intracellular, light-evok