In which retinal layer do photoreceptors and bipolar cells form synapses that are modulated by horizontal cells?

• A. Inner Nuclear Layer
• B. Outer Plexiform Layer
• C. Inner Plexiform Layer
• D. Ganglion Cell Layer

Answer: (B)

The outer plexiform layer is where the first synapses in the visual pathway form between photoreceptors and bipolar cells, and it’s also where horizontal cells reside to modulate those connections. Horizontal cells provide lateral feedback in this layer, shaping the signal as it moves from photoreceptors to bipolar cells and creating the center-surround receptive fields that enhance contrast. In contrast, the inner plexiform layer is where bipolar cells connect to ganglion and amacrine cells, the inner nuclear layer contains the cell bodies of bipolar, horizontal, and amacrine cells, and the ganglion cell layer houses ganglion cell bodies.