2. 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

3. Receptive fields of sensory neurons The physical area over which appropriate modality energy can influence the membrane potential of the nerve cell.

4. Fine 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.

5. Lateral Inhibition:What Does it do for you?  1111111111111111 1111111111111111 1111111111111111 1110001111111111 1110901111111111 1110001111111111 1111111111111111 1111111111111111 1111111111111111 1111111111111111 It Enhances Edges!!

6. Mach Bands

7. Building a light sensor Retinal Physiology : from perceptions to spike trains to photon capture, an overview

8. Tartuferi 1887 Ganglion cell layer Amacrine cells Bipolar Cells Horizontal Cells Rod and Cone Photoreceptors

9. Key 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. lateral inhibtion center-surround organization  Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtion and center-surround organization.  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. lateral inhibtion center-surround organization  Horizontal and amacrine cell form lateral connections and are critical for lateral inhibtion and center-surround organization. Dr. Tim Kraft twkraft@uab.edu

10. Key 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.

11. Retina anatomy - overview

12. Center Surround receptive fields require lateral interactions. Ganglion cell Receptive Fields

13. Center from on (+) bipolar Surround from off (-) bipolars - + - Antagonistic Center Vs. Surround

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

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

16. 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)

17. Cone(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)

18. Light is the ligand that triggers activation of the enzyme.

19. Biochemistry of Phototransduction Rhodopsin is the classic example of a G-protein coupled receptor. (ligand = photons) Rhodopsin is the classic example of a G-protein coupled receptor. (ligand = photons) RODS: High gain means high sensitivity (But takes time to develop). RODS: High gain means high sensitivity (But takes time to develop). CONES Smaller Responses, due to lower sensitivity (low gain) are over faster resulting in higher... CONES Smaller Responses, due to lower sensitivity (low gain) are over faster resulting in higher... Rhodopsin is the classic example of a G-protein coupled receptor. (ligand = photons) Rhodopsin is the classic example of a G-protein coupled receptor. (ligand = photons) RODS: High gain means high sensitivity (But takes time to develop). RODS: High gain means high sensitivity (But takes time to develop). CONES Smaller Responses, due to lower sensitivity (low gain) are over faster resulting in higher... CONES Smaller Responses, due to lower sensitivity (low gain) are over faster resulting in higher...

21. Photocurrent & Photovoltages Graded responses (no spikes) Photoreceptors are partially depolarized in the dark (due to an influx of Na + and Ca 2+ ions). Photoreceptors are partially depolarized in the dark (due to an influx of Na + and Ca 2+ ions). Light shuts off the influx, thus the cells hyperpolarize and... Light shuts off the influx, thus the cells hyperpolarize and... Neurotransmitter is released constantly in the dark and this release is attenuated by light!!!! (GLUTAMATE) Neurotransmitter is released constantly in the dark and this release is attenuated by light!!!! (GLUTAMATE) Photoreceptors are partially depolarized in the dark (due to an influx of Na + and Ca 2+ ions). Photoreceptors are partially depolarized in the dark (due to an influx of Na + and Ca 2+ ions). Light shuts off the influx, thus the cells hyperpolarize and... Light shuts off the influx, thus the cells hyperpolarize and... Neurotransmitter is released constantly in the dark and this release is attenuated by light!!!! (GLUTAMATE) Neurotransmitter is released constantly in the dark and this release is attenuated by light!!!! (GLUTAMATE)

22. Rod vs. Cone Kinetic & Sensitivity

23. Themes of retinal circuitry Divergent wiring (on/off pathways). Divergent wiring (on/off pathways). Convergent wiring. (Greatest summation) Highest sensitivity (rod pathway) Convergent wiring. (Greatest summation) Highest sensitivity (rod pathway) Highest visual acuity and fidelity of signals carrying that message requires requires a private line (Midget system). Highest visual acuity and fidelity of signals carrying that message requires requires a private line (Midget system). Divergent wiring (on/off pathways). Divergent wiring (on/off pathways). Convergent wiring. (Greatest summation) Highest sensitivity (rod pathway) Convergent wiring. (Greatest summation) Highest sensitivity (rod pathway) Highest visual acuity and fidelity of signals carrying that message requires requires a private line (Midget system). Highest visual acuity and fidelity of signals carrying that message requires requires a private line (Midget system).

24. Private Line Divergence Convergence

25. Themes of retinal circuitry Horizontal Cells and Amacrine cells provide lateral pathways in the retina. Horizontal Cells and Amacrine cells provide lateral pathways in the retina. Feedback and feed forward synaptic interactions add flexibility and complexity Feedback and feed forward synaptic interactions 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 adaptation) Network gain control (light/dark adaptation) Horizontal Cells and Amacrine cells provide lateral pathways in the retina. Horizontal Cells and Amacrine cells provide lateral pathways in the retina. Feedback and feed forward synaptic interactions add flexibility and complexity Feedback and feed forward synaptic interactions 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 adaptation) Network gain control (light/dark adaptation)

26. On and Off pathways Divergent wiring - cone hyperpolarizes to light Divergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different responses.(receptor biochemistry) Same neurotransmitter changes, different responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON ganglion cells (SPIKING INCREASES) On bipolar: sign inverting feeds onto ON ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off ganglion cells (SPIKING Diminishes) Off bipolar: sign conserving feeds onto Off ganglion cells (SPIKING Diminishes) Divergent wiring - cone hyperpolarizes to light Divergent wiring - cone hyperpolarizes to light Same neurotransmitter changes, different responses.(receptor biochemistry) Same neurotransmitter changes, different responses.(receptor biochemistry) On bipolar: sign inverting feeds onto ON ganglion cells (SPIKING INCREASES) On bipolar: sign inverting feeds onto ON ganglion cells (SPIKING INCREASES) Off bipolar: sign conserving feeds onto Off ganglion cells (SPIKING Diminishes) Off bipolar: sign conserving feeds onto Off ganglion cells (SPIKING Diminishes)

27. The Off pathway Light hyperpolarizes photoreceptors. Light hyperpolarizes 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 down. Spike frequency (rate) goes down. Light hyperpolarizes photoreceptors. Light hyperpolarizes 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 down. Spike frequency (rate) goes down.

28. The On pathway Light hyperpolarizes photoreceptors. Light hyperpolarizes 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 photoreceptors. Light hyperpolarizes 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.

30. Building Receptive Fields Center and surround organizations Center and surround organizations Begin at the bipolar cell level via horizontal cell lateral synapses Begin at the bipolar cell level via horizontal cell lateral synapses More complex at the Ganglion cell via Amacrine cell synapses More complex at the Ganglion cell via Amacrine cell synapses On or Off responses (anatomical correlation with sublaminae of IPL) On or Off responses (anatomical correlation with sublaminae of IPL) Center and surround organizations Center and surround organizations Begin at the bipolar cell level via horizontal cell lateral synapses Begin at the bipolar cell level via horizontal cell lateral synapses More complex at the Ganglion cell via Amacrine cell synapses More complex at the Ganglion cell via Amacrine cell synapses On or Off responses (anatomical correlation with sublaminae of IPL) On or Off responses (anatomical correlation with sublaminae of IPL)

32. ` `

33. Bipolar Cell morphology/physiolgy Rod vs. Cone anatomical connection-input Rod vs. Cone anatomical connection-input Midget vs. diffuse receptive field size Midget vs. diffuse receptive field size On vs. Off On vs. Off Physiological subtype Physiological subtype With anatomical correlations With anatomical correlations On : Middle element of invaginating synapse On : Middle element of invaginating synapse On: output synapse in the inner half of IPL On: output synapse in the inner half of IPL Off: Flat synapse Off: Flat synapse Off: output synapse in the OUTER half of IPL Off: 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 synapses High contrast gain at input synapses Rod vs. Cone anatomical connection-input Rod vs. Cone anatomical connection-input Midget vs. diffuse receptive field size Midget vs. diffuse receptive field size On vs. Off On vs. Off Physiological subtype Physiological subtype With anatomical correlations With anatomical correlations On : Middle element of invaginating synapse On : Middle element of invaginating synapse On: output synapse in the inner half of IPL On: output synapse in the inner half of IPL Off: Flat synapse Off: Flat synapse Off: output synapse in the OUTER half of IPL Off: 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 synapses High contrast gain at input synapses

34. Several distinct morphological types have been identified. Some match physiological types Others remain unclassified

35. 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  A II  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  A II  Cone Bp  cone ganglion cells etc. etc.

36. 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

37. A II amacrine cell

38. 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). SSpatial information (by anatomical mapping to topographic cortex) TTemporal codes FFunctional mapping (color signals to color cortex, motion signals to motion cortex etc.) CCross correlation between neighboring cells or groups of cells (new horizons).

39. Building 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

40. Local specializations

41. Photoreceptor distribution Fig 15.12

42. 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)