- On- center bipolar cells are Inhibited by glutamate
- Light in the center of their receptive field causes less glutamate release from photoreceptors—> light excites on-center bipolar cells
- Excitation causes glutamate release from bipolar cells
- On-center ganglion cells are then excited and send signals to higher visual centers

On-center bipolar cells response to light

- Off-center bipolar cells are excited by glutamate
- Turning the light off in the center of the receptive field causes glutamate release from photoreceptors, and excites off-center bipolar cells
- Excitation causes glutamate release from bipolar cells
- Off-center ganglion cells are then excited and send signals to higher visual centers

Off-center bipolar cells response to light

- Light always hyper polarizes photoreceptors (rods and cones)
- Hyperpolarization causes the photoreceptors to release less glutamate
- Decreased glutamate release excites some retinal neurons and inhibits others

University of Michigan - Ann Arbor

Neurons in the retina and LGN have receptive fields that consist of a circular central area and a ring around it.

Concentric receptive fields of retinal and lateral geniculate nucleus (LGN) neurons

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

- The LGN is a part of the thalamus that transmits visual information
- Receives information from the optic tract
- Sends information to the occipital lobe
- Some axons terminate in the primary visual cortex of the occipital lobe-- these are called optic radiations

Lateral geniculate nucleus (LGN)

- The LGN is made of six main layers 
- All layers contain concentric receptive fields
- The four outer (dorsal) layers are made of small cells (parvocellular)
- The two inner (ventral) layers are made of large cells (magnocellular)

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