Which of the following is NOT true regarding horizontal cells?

• A. They provide lateral inhibition to information reaching bipolar cells
• B. They primarily synapse within the IPL
• C. They are joined together with horizontal cells via gap junctions
• D. They primarily communicate with photoreceptors and bipolar cells

Answer: (B)

The concept here is how horizontal cells shape retinal signals through lateral interactions in the outer retina. Horizontal cells sit in the outer plexiform layer, where they receive input from photoreceptors and connect to both photoreceptors and bipolar cells to modulate their output. They are also connected to other horizontal cells via gap junctions, forming a network that spreads signals laterally to create center-surround antagonism and sharpen contrast.

Thus, they provide lateral inhibition that affects information reaching bipolar cells, and they primarily communicate with photoreceptors and bipolar cells. They are indeed joined with other horizontal cells by gap junctions. The statement that is not true is that they primarily synapse within the inner plexiform layer; horizontal cells do not reside there—they are located in the outer plexiform layer.