Retinal Physiology Vocabulary

Retinal Physiology Vocabulary

Receptive Field Spatial summation Temporal summation Convergent wiring Divergent wiring

Lateral inhibition Feedback/Feedforward circuit Edge enhancement

Center/surround organization On vs. Off pathways in Retina

Graded responses vs. Action Potentials

Receptive Field Spatial summation Temporal summation Convergent wiring Divergent wiring

Lateral inhibition Feedback/Feedforward circuit Edge enhancement

Center/surround organization On vs. Off pathways in Retina

Graded responses vs. Action Potentials

Receptive fields of sensory neurons

The physical area over which appropriate modality energy can influence the membrane potential of the nerve cell.

The physical area over which appropriate modality energy can influence the membrane potential of the nerve cell.

Fine Touch DiscriminationFine Touch Discrimination

Note the receptive field size varies with location on the skin.

Two point discrimination is linked to receptive field diameter.

Different modalities (fine touch, cold pain) can have different receptive field sizes in the same location.

Note the receptive field size varies with location on the skin.

Two point discrimination is linked to receptive field diameter.

Different modalities (fine touch, cold pain) can have different receptive field sizes in the same location.

Lateral Inhibition:What Does it do for

you?

Lateral Inhibition:What Does it do for

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It EnhancesEdges!!

Mach BandsMach Bands

Building a light sensorBuilding a light sensor

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are needed to see this picture.

Retinal Physiology: from perceptionsto spike trains to photon capture, an overview

Tartuferi 1887Tartuferi 1887

Ganglion cell layer Amacrine cells

Bipolar Cells

Horizontal Cells

Rod and Cone Photoreceptors

Key points to rememberKey points to remember

Duel photoreceptors system (rods & cones) extend the range of visual function.

The minimal direct pathway for a signal is photoreceptor to bipolar cell to ganglion cell.

Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtionlateral inhibtion and center-surround center-surround organizationorganization.

Duel photoreceptors system (rods & cones) extend the range of visual function.

The minimal direct pathway for a signal is photoreceptor to bipolar cell to ganglion cell.

Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtionlateral inhibtion and center-surround center-surround organizationorganization.

Dr. Tim Kraft twkraft@uab.edu

Key points to rememberKey points to remember

The retina is interested in contrast differences, edges, light vs. dark. The on-off pathways are critical for

making these comparisons. This division begins at the bipolar cell level.

The center-surround receptive field is a key feature of retinal output. It starts at the bipolar cells.

Perceptual limits are set at various levels of the nervous system.

The retina is interested in contrast differences, edges, light vs. dark. The on-off pathways are critical for

making these comparisons. This division begins at the bipolar cell level.

The center-surround receptive field is a key feature of retinal output. It starts at the bipolar cells.

Perceptual limits are set at various levels of the nervous system.

Retina anatomy - overview

Retina anatomy - overview

Center Surround receptive fields require lateral interactions.

Ganglion cell Receptive Fields

Ganglion cell Receptive Fields

Center from on (+) bipolarSurround from off (-) bipolars

-+-

Antagonistic Center Vs. Surround

Ganglion cell Receptive Fields

Figure 28-3Summary of ganglion cell receptive fields, showing the spike trains generated by the stimulus.

PhotoreceptorsPhotoreceptors

Duality (rods and cones) permits specialization into two systems (1) for high sensitivity and (2) for spatial and temporal sensitivity (plus color).

Duality (rods and cones) permits specialization into two systems (1) for high sensitivity and (2) for spatial and temporal sensitivity (plus color).

Rod photoreceptor (system)

Rod photoreceptor (system)

95% of photoreceptor in human eye

Single photon sensitivity (amazing feat)

High degree of spatial summation . . . Therefore LOW spatial acuity

Slow time-to-peak, slow recovery . . . Therefore LOW temporal resolution

Dark, starlight, moonlight (2.5 log units)

95% of photoreceptor in human eye

Single photon sensitivity (amazing feat)

High degree of spatial summation . . . Therefore LOW spatial acuity

Slow time-to-peak, slow recovery . . . Therefore LOW temporal resolution

Dark, starlight, moonlight (2.5 log units)

Cone(system) functionCone(system) function

In foveate animals the overwhelming majority of visual behavior depends on this minute (<1%) patch of retina. (Tiny area of high spatial acuity).

Fast response time, but insensitive.

Wide range of adaptation (6+ Log Units)

In foveate animals the overwhelming majority of visual behavior depends on this minute (<1%) patch of retina. (Tiny area of high spatial acuity).

Fast response time, but insensitive.

Wide range of adaptation (6+ Log Units)

Light is the ligand that triggers activation of the enzyme.

Biochemistry of PhototransductionBiochemistry of Phototransduction

Rhodopsin is Rhodopsin is thethe classic example of a classic example of a G-protein coupled receptor. (ligand = G-protein coupled receptor. (ligand = photons)photons)

RODS: High gain means high sensitivity RODS: High gain means high sensitivity (But takes time to develop).(But takes time to develop).

CONES Smaller Responses , due to CONES Smaller Responses , due to lower sensitivity (low gain) are over lower sensitivity (low gain) are over faster resulting in higher . . . faster resulting in higher . . .

Rhodopsin is Rhodopsin is thethe classic example of a classic example of a G-protein coupled receptor. (ligand = G-protein coupled receptor. (ligand = photons)photons)

RODS: High gain means high sensitivity RODS: High gain means high sensitivity (But takes time to develop).(But takes time to develop).

CONES Smaller Responses , due to CONES Smaller Responses , due to lower sensitivity (low gain) are over lower sensitivity (low gain) are over faster resulting in higher . . . faster resulting in higher . . .

Photocurrent & Photovoltages Graded responses (no spikes)Photocurrent & Photovoltages Graded responses (no spikes)

Photoreceptors are partially depolarized Photoreceptors are partially depolarized in the dark (due to an influx of Nain the dark (due to an influx of Na++ and and CaCa2+2+ ions). ions).

Light shuts off the influx, thus the cells Light shuts off the influx, thus the cells hyperpolarize and . . . hyperpolarize and . . .

Neurotransmitter is released constantly Neurotransmitter is released constantly in the dark and this release is in the dark and this release is attenuated by light!!!! (GLUTAMATE)attenuated by light!!!! (GLUTAMATE)

Photoreceptors are partially depolarized Photoreceptors are partially depolarized in the dark (due to an influx of Nain the dark (due to an influx of Na++ and and CaCa2+2+ ions). ions).

Light shuts off the influx, thus the cells Light shuts off the influx, thus the cells hyperpolarize and . . . hyperpolarize and . . .

Neurotransmitter is released constantly Neurotransmitter is released constantly in the dark and this release is in the dark and this release is attenuated by light!!!! (GLUTAMATE)attenuated by light!!!! (GLUTAMATE)

Rod vs. Cone Kinetic & SensitivityRod vs. Cone Kinetic & Sensitivity

Themes of retinal circuitryThemes of retinal circuitry

Divergent wiring (on/off pathways).Divergent wiring (on/off pathways).

Convergent wiring. (Greatest Convergent wiring. (Greatest summation) Highest sensitivity (rod summation) Highest sensitivity (rod pathway)pathway)

Highest visual acuity and fidelity of Highest visual acuity and fidelity of signals carrying that message requires signals carrying that message requires requires a private line (Midget system).requires a private line (Midget system).

Divergent wiring (on/off pathways).Divergent wiring (on/off pathways).

Convergent wiring. (Greatest Convergent wiring. (Greatest summation) Highest sensitivity (rod summation) Highest sensitivity (rod pathway)pathway)

Highest visual acuity and fidelity of Highest visual acuity and fidelity of signals carrying that message requires signals carrying that message requires requires a private line (Midget system).requires a private line (Midget system).

Private LinePrivate Line DivergenceDivergence ConvergenceConvergence

Private LinePrivate Line DivergenceDivergence ConvergenceConvergence

Themes of retinal circuitry Themes of retinal circuitry

Horizontal Cells and Amacrine cells Horizontal Cells and Amacrine cells provide lateral pathways in the retina.provide lateral pathways in the retina.

Feedback and feed forward synaptic Feedback and feed forward synaptic interactions add flexibility and complexityinteractions add flexibility and complexity

Spatial filters (Lateral inhibition)Spatial filters (Lateral inhibition)Temporal filters (Directional selectivity)Temporal filters (Directional selectivity)Network gain control (light/dark Network gain control (light/dark

adaptation)adaptation)

Horizontal Cells and Amacrine cells Horizontal Cells and Amacrine cells provide lateral pathways in the retina.provide lateral pathways in the retina.

Feedback and feed forward synaptic Feedback and feed forward synaptic interactions add flexibility and complexityinteractions add flexibility and complexity

Spatial filters (Lateral inhibition)Spatial filters (Lateral inhibition)Temporal filters (Directional selectivity)Temporal filters (Directional selectivity)Network gain control (light/dark Network gain control (light/dark

adaptation)adaptation)

On and Off pathwaysOn and Off pathways

Divergent wiring - cone hyperpolarizes to lightDivergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different Same neurotransmitter changes, different

responses.(receptor biochemistry)responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON On bipolar: sign inverting feeds onto ON

ganglion cells (SPIKING INCREASES)ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off Off bipolar: sign conserving feeds onto Off

ganglion cells (SPIKING Diminishes)ganglion cells (SPIKING Diminishes)

Divergent wiring - cone hyperpolarizes to lightDivergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different Same neurotransmitter changes, different

responses.(receptor biochemistry)responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON On bipolar: sign inverting feeds onto ON

ganglion cells (SPIKING INCREASES)ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off Off bipolar: sign conserving feeds onto Off

ganglion cells (SPIKING Diminishes)ganglion cells (SPIKING Diminishes)

The Off pathwayThe Off pathway Light hyperpolarizes Light hyperpolarizes

photoreceptors.photoreceptors. Transmitter release goes down.Transmitter release goes down. Off bipolar cells hyperpolarize.Off bipolar cells hyperpolarize. Transmitter release goes down.Transmitter release goes down. Ganglion cells hyperpolarize.Ganglion cells hyperpolarize. Spike frequency (rate) goes Spike frequency (rate) goes

down.down.

Light hyperpolarizes Light hyperpolarizes photoreceptors.photoreceptors.

Transmitter release goes down.Transmitter release goes down. Off bipolar cells hyperpolarize.Off bipolar cells hyperpolarize. Transmitter release goes down.Transmitter release goes down. Ganglion cells hyperpolarize.Ganglion cells hyperpolarize. Spike frequency (rate) goes Spike frequency (rate) goes

down.down.

The On pathwayThe On pathway Light hyperpolarizes Light hyperpolarizes

photoreceptors.photoreceptors. Transmitter release goes down.Transmitter release goes down. On bipolar cells depolarize.On bipolar cells depolarize. Transmitter release goes up.Transmitter release goes up. Ganglion cells depolarize.Ganglion cells depolarize. Spike frequency (rate) goes up.Spike frequency (rate) goes up.

Light hyperpolarizes Light hyperpolarizes photoreceptors.photoreceptors.

Transmitter release goes down.Transmitter release goes down. On bipolar cells depolarize.On bipolar cells depolarize. Transmitter release goes up.Transmitter release goes up. Ganglion cells depolarize.Ganglion cells depolarize. Spike frequency (rate) goes up.Spike frequency (rate) goes up.

Building Receptive FieldsBuilding Receptive Fields

Center and surround organizationsCenter and surround organizations Begin at the bipolar cell level via horizontal Begin at the bipolar cell level via horizontal

cell lateral synapsescell lateral synapses More complex at the Ganglion cell via Amacrine More complex at the Ganglion cell via Amacrine

cell synapsescell synapses

On or Off responses (anatomical On or Off responses (anatomical correlation with sublaminae of IPL)correlation with sublaminae of IPL)

Center and surround organizationsCenter and surround organizations Begin at the bipolar cell level via horizontal Begin at the bipolar cell level via horizontal

cell lateral synapsescell lateral synapses More complex at the Ganglion cell via Amacrine More complex at the Ganglion cell via Amacrine

cell synapsescell synapses

On or Off responses (anatomical On or Off responses (anatomical correlation with sublaminae of IPL)correlation with sublaminae of IPL)

`̀

Bipolar Cell morphology/physiolgyBipolar Cell morphology/physiolgy Rod vs. Cone Rod vs. Cone anatomical connection-inputanatomical connection-input Midget vs. diffuse Midget vs. diffuse receptive field sizereceptive field size On vs. Off On vs. Off

Physiological subtypePhysiological subtype With anatomical correlationsWith anatomical correlations

On : Middle element of invaginating synapseOn : Middle element of invaginating synapse On: output synapse in the inner half of IPLOn: output synapse in the inner half of IPL Off: Flat synapseOff: Flat synapse Off: output synapse in the OUTER half of IPLOff: output synapse in the OUTER half of IPL

Unique Blue cone bipolar (non-midget)Unique Blue cone bipolar (non-midget) High contrast gain at input synapsesHigh contrast gain at input synapses

Rod vs. Cone Rod vs. Cone anatomical connection-inputanatomical connection-input Midget vs. diffuse Midget vs. diffuse receptive field sizereceptive field size On vs. Off On vs. Off

Physiological subtypePhysiological subtype With anatomical correlationsWith anatomical correlations

On : Middle element of invaginating synapseOn : Middle element of invaginating synapse On: output synapse in the inner half of IPLOn: output synapse in the inner half of IPL Off: Flat synapseOff: Flat synapse Off: output synapse in the OUTER half of IPLOff: output synapse in the OUTER half of IPL

Unique Blue cone bipolar (non-midget)Unique Blue cone bipolar (non-midget) High contrast gain at input synapsesHigh contrast gain at input synapses

Several distinct Several distinct morphological types morphological types have been have been identified.identified.

Some match Some match physiological typesphysiological types

Others remain Others remain unclassifiedunclassified

Several distinct Several distinct morphological types morphological types have been have been identified.identified.

Some match Some match physiological typesphysiological types

Others remain Others remain unclassifiedunclassified

The Rod piggyback-pathway

The Rod piggyback-pathway

Without a rod-specific ganglion cells, how does the brain receive rod signals?

Through the AII amacrine cells, rods piggy-back their signal through the cone pathway.

Rod Rod Bp AII Cone Bp cone ganglion cells etc. etc.

Without a rod-specific ganglion cells, how does the brain receive rod signals?

Through the AII amacrine cells, rods piggy-back their signal through the cone pathway.

Rod Rod Bp AII Cone Bp cone ganglion cells etc. etc.

Rod Pathway

Rod Pathway No Direct

Ganglion cell output.

Rod bipolar to amacrine cell

A combination of electric and chemical synapses

Output through cone G-cells

No Direct Ganglion cell output.

Rod bipolar to amacrine cell

A combination of electric and chemical synapses

Output through cone G-cells

AII amacrine cellAII amacrine cell

How to spikes encode information?

How to spikes encode information?

Spatial information (by anatomical mapping to topographic cortex)

Temporal codes Functional mapping (color

signals to color cortex, motion signals to motion cortex etc.)

Cross correlation between neighboring cells or groups of cells (new horizons).

Spatial information (by anatomical mapping to topographic cortex)

Temporal codes Functional mapping (color

signals to color cortex, motion signals to motion cortex etc.)

Cross correlation between neighboring cells or groups of cells (new horizons).

Building Receptive FieldsBuilding Receptive Fields

Center and surround organizations

On or Off responses (anatomical correlation with sublaminae of IPL)

Transient and sustained physiology

Center and surround organizations

On or Off responses (anatomical correlation with sublaminae of IPL)

Transient and sustained physiology

Local specializations Local specializations

Photoreceptor distribution

Photoreceptor distribution

Fig 15.12

Specializations of the fovea

Specializations of the fovea

Inner retinal layers do not exist here (pushed aside)

No retinal blood vessels

No rod photoreceptos

No blue-sensitive cones (tritanopia - blue blind)

Inner retinal layers do not exist here (pushed aside)

No retinal blood vessels

No rod photoreceptos

No blue-sensitive cones (tritanopia - blue blind)