Retinal Circuit LGN Retinal circuitry underlying the RGC

Retinal Circuit, LGN • Retinal circuitry underlying the RGC receptive field • Projection from retina to LGN • LGN layers • LGN receptive fields

Direct pathway: Photo receptor Bipolar RGC +: excitatory synapse, preserve response direction -: inhibitory synapse, flip response direction Direct pathway is responsible to the RF center

Indirect pathway mediated by horizontal is responsible to the RF surround There are other indirect pathway mediated by amacrine cells

Summary of retinal circuit Direct pathway Indirect pathway Pathways mediated by amacrine cells

Projection from retina to LGN fixation point fovea • Nasal RGC: axons crossover, project to contralateral LGN • Temporal RGC: axons stay on the same side (ipsilateral) • Left visual field: right LGN, right V 1 • Right visual field: left LGN, left V 1

LGN layers

• Parvocellular layers: 3 -6 • Magnocellular layers: 1, 2 (input from P cells in retina) • Contralateral eye: 1, 4, 6 • Ipsilateral eye: 2, 3, 5 • But all LGN layers represent contralateral visual field!

Lesion studies

• Parvocellular layers: small cells, color sensitive, high spatial resolution (small RF), low temporal resolution (does not see fast flickers of light). They receive inputs from P type RGC cells • Magnocellular layers: large cells, color blind, low spatial resolution (large RF), high temporal resolution (good for processing motion stimuli). They receive inputs from M type RGC cells

Anatomical segregation of M and P pathways

LGN RF: similar to RGC RF, ON center/OFF surround or OFF center/ON surround This is a spatiotemporal RF

Knowing the RF allows you to predict responses to arbitrary visual stimuli, including natural movies

Knowing the RF also allows you to reconstruct visual stimuli from the recorded responses Reconstructed From ~ 200 LGN neurons Original