Functions of the retina

Retina performs five important jobs: 1. transduction 2. wavelength encoding 3. light/dark adaptation & chromatic adaptation 4. spatial filtering 5. data compression

Neural Pigmented cell circuitry in Rod the retina Cone

Horizontal cell Amacrine cell Bipolar cell

Ganglion cell

Neural circuits: rod pathway Neural circuits in the retina (monkey rod pathway)

Rod bipolar

AII amacrines

Parallel pathways (processing streams)

1. Anatomically distinct 2. Physiologically/functionally distinct 3. Complete coverage 4. Recombine

Example: rods and cones

Some retinal ganglion cell types

midget small bistratified

parasol Parallel pathways: ganglion cells

Parasol ganglion cell: Midget ganglion cell: 1. Inputs from many 1. Inputs from few (or photoreceptors one) photoreceptors 2. Fast/transient 2. Slow/sustained responses responses 3. Poor spatial resolution 3. High spatial resolution 4. Combine all cones (“color blind”)

Ganglion cell receptive fields & inputs from cone lattice

Field et al., Nature (2010)

Ganglion cell mosaics

Field et al., Nature (2010) Retinal ganglion cell responses

on-center RGC off-center RGC

stimulus: on off stimulus: on off

Retinal ganglion cell measurements (Kuffler 1950s)

Receptive fields: center-surround organization Receptive Fields

- - - + - + + + - - + - + - + + + - - + - + + - + - + - - + - - + + - - - + + +

On-center, Off-surround Off-center, On-surround

Center-surround circuitry in the retina On-off layer segregation

Linearity of RGC responses

Linearity of RGC responses Linear receptive field model

Photoreceptors

Bipolar cells

+ - - Ganglion cell

Linear receptive field model

Neural image Neural image

Input image “Neural image” (cornea) (retinal ganglion cells)

Center-surround receptive fields: emphasize edges.

‘On’ and “off” responses

Stimulus Receptive field x

t

Functions of the retina

Retina performs five important jobs: 1. transduction 2. wavelength encoding 3. light/dark adaptation & chromatic adaptation 4. spatial filtering 5. data compression Retinal inhomogeneity

Simulations of the high spatial resolution in central vision coupled with the blurry low spatial resolution in the periphery.

Distribution of rods and cones

Foveal cone mosaic Near periphery photoreceptor mosaic

rods

cones

Dendritic fields increase with eccentricity

(Dacey, 1993; human)

Parasol

Small bistratified

Midget Dendritic field diameter (microns) diameter field Dendritic

Retinal eccentricity (mm)

Diseases of the retina

macular degeneration

retinitis pigmentosa Retinal implants