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An amacrine cell is a retinal interneuron that modifies signaling in the inner retina, including interactions between retinal bipolar cells and retinal ganglion cells. Different types contribute different spatial, temporal and inhibitory interactions.

This diversity makes the label an anatomical and circuit category rather than one universal computation. Comparing responses before and after a specific connection is perturbed can test a proposed function more directly than observing that an amacrine cell responds to moving light.

A descending motor pathway carries signals from more rostral neural centers toward brainstem or spinal circuits contributing to movement. Its effect depends on intervening interneurons and motor neurons. An anatomical projection is therefore not necessarily a direct command to one muscle.

A retinal interneuron contributing lateral interactions among photoreceptor signals and spatial context. Its participation in a circuit does not imply that every perceptual surround effect originates at that one cell type.

An interneuron is a neuron acting within a neural circuit to connect and transform signals between other neurons. Many interneurons have local connections, although the category is defined functionally and includes diverse cell types. An interneuron is not automatically inhibitory: excitatory and inhibitory signalling depend on transmitter, receptor and cellular context. ^[ref]

In a reflex circuit, an inhibitory interneuron can couple activation of one motor pathway to suppression of an opposing one. This gives a concrete computational function: the circuit coordinates two outputs instead of simply forwarding a sensory signal unchanged. Recording one interneuron's activity establishes participation, while changing that activity and measuring the circuit response tests its causal contribution.

A retinal interneuron relaying photoreceptor signals toward ganglion-cell circuits. ON and OFF types differ in how changes in photoreceptor output affect their responses.