The document summarizes retinal anatomy and modeling. It discusses the layers of the retina including photoreceptors, bipolar cells, horizontal cells, amacrine cells, and ganglion cells. It describes the connections between these cells, including chemical synapses and electrical gap junctions. The goal of the author's PhD is to improve an existing retinal model to produce synchronized spike outputs from ganglion cells by adding connections between ganglion cells and between ganglion and amacrine cells.

2. Retina: Anatomy and modeling
Hassan Nasser
Neuromathcomp - INRIA

3. Context
• Presentation of two articles:
– T. Gollisch, M. Meister: Eye Smarter than Scientists
Believed: Neural Computations in Circuits of the
Retina (2009).
– Helga Kolb: How the Retina Works (2003).
• Discussion in the scope of my PhD: How to
reproduce the retinal responses.

4. Visual pathways (2 min) Eye (2 min) Retina (5 min)
Discussion
3 min Model (3 min) Interaction between cells (7 min)

5. What is a Visual pathway?
- It’s a set of cells bodies and
nerves conducting impulses from
the eye to the cerebral cortex
- Reception of external images
and transport of visual
information
Retina Optic nerve Visual Cortex
V1, V2…
(ganglion cells)
light

6. Eye
Three different layers:
1- The external layer, formed
by the sclera, pupil and
cornea.
2- The intermediate layer,
divided into two parts:
anterior (iris, lens and ciliary
body) and posterior (choroid).
3- The internal layer, or the
sensory part of the eye, the
retina.

7. Retina
-The retina is approximately 0.5 mm thick and lines the back of the
eye.
- Optic nerve contains: RGC axons + Blood vessels

8. Retina
Absorption of light
Light direction
All vertebrate retinas are composed of three layers of nerve cell bodies
and two layers of synapses. The retina is designed according to the life
style!. EX: Fish, Frog, Turtle have 5 types of cones  Colored vision.

9. • Layers of nerve cells:
– Outer nuclear layer
contains cell bodies of
the rods and cones.
– Inner nuclear layer
contains cell bodies of
the bipolar, horizontal
and amacrine cells.
– Ganglion cell layer
contains cell bodies of
ganglion cells and
displaced amacrine cells
• Layers of synapses:
– Outer plexiform layer (OPL)
where connections between
rod and cones
– Inner plexiform layer (IPL),
and it functions as a relay
station for the vertical-
information-carrying nerve
cells, the bipolar cells, to
connect to ganglion cells.

10. About retinal cells
• Photoreceptors.
• Bipolar cells.
• Horizontal Cells.
• Amacrine cells.
• Ganglion cells.

11. Photoreceptors
• 2-3 types of cones
– Cones are concentrated in the fovea centralis.
– 6-7 millions ("red" cones (64%), "green" cones (32%),
and "blue" cones (2%))
– Sensitive to colors.
– Visual acuity.
• 1 types of Rods.
– ~ 120 millions.
– More sensitive (1000 times) than cones but not
sensitive to the colors  Night vision.

12. Day Night

13. Cones & Rods
When light is shone onto a
photoreceptor, the photoreceptor
hyperpolarizes and reduces the
release of glutamate.

14. Bipolar - Horizontal – Amacrine - Ganglion

15. The retina is:
-A photo transducer that transforms
photons to current?
-The retina is a processor to detect
image features (motion, contrast,
edges)?
-The retina is a sophisticated processor
that exceed the last two expectations?
Retina smarter than scientists believed!
More than 50 types of connected cells.
FM Signal

16. Connections between retinal cells
• Introduction:
– Synapse.
– Action potential.
– Graded action potential.
• Connection types:
– Chemical synapses.
– Electrical synapses.

17. (All-or-none principle)
Chemical Synapse
-The action potential arrives in the Pre synaptic cells (Indicator: Increasing of
calcium concentration inside)
-Releasing of neurotransmitters from their vesicles in the synaptic cleft.
-Fixation of neurotransmitters on the receptor of postsynaptic cleft.
-Triggering of the action potential in the post synaptic cell.
In the retina: Only RGC obeys to All-or-none principle. Others shows graded behavior
(the postsynaptic potential is proportional to the presynaptic potential)

18. Electrical connections – Gap junctions
-Allow direct and faster connection between two cells.
-Resistance for current depends on several parameters (Acidity degree,
Calcium concentration, temperature, …).
-Simple model = Resistance. Complicated model: Current transfer
taking into account the majority of parameters to produce biological
plausibility.

19. Let’s see how retina works:
Connections roles in the information
transport and parallel processing.

20. Synaptic connection
Mouse retina

21. Gap junctions

22. Functional role of Gap Junction
- Gap junctions exists between cells of
every type in the retina.
Stewart A et al. 2009

23. … Between Photoreceptors
• Blurring of visual signal.
• Reduction in acuity.
• Coupling between photoreceptors sums the
correlated visual signal and attenuates the
asynchronous noise which comes from photo-
chemical transduction (improve the SNR by
80%). Stewart A et al. 2009

24. … Between Ganglion cells
• Ganglion-Ganglion gap junctions (fast
excitation < 2ms  narrow spiking frequency
distribution).
• Ganglion-Amacrine gap junctions (slower
connections … broad distribution).
• Synchronization of spike outputs.

25. The aim of my PhD is to improve the
existent retina model (VirtualRetina) in
order to produce the retinal
synchronized output. How? … In the
discussion.

26. Circuit modeling of retinal function:
How to represent the retinal function
in simple electrical circuits?
• Light detection.
• Differential motion.

27. Light detection
At the post-synaptic gate of photoreceptor, we have: Signal + noise.
The synaptic connection between the photoreceptors and the bipolar cell is
equivalent to: A temporal filter followed by a threshold operation.
The filtered signals are given to the bipolar cell each through a dendrite connection:
The potential in the bipolar cell will be the summation of all these signals.

28. Differential motion
- Coding: Making the difference between the periphery signal (fb) and the
center signal.
- Same signal  same motion. Different signal  differential motion.

29. Virtual Retina
-Large scale simulation (> 10000
cells).
-Implementation of functional
retinal events.
-A compromise between
computational cost and biological
plausibility.
-Spike outputs are not
synchronized.

31. Gollisch et al. 2009

32. How to implement the
synchronization?
• Adding connection/Gap-Junctions between
Ganglion-Ganglion cells and Ganglion-
Amacrine cells.
• How to add these connection?  Study the
statistics of real acquisition for vertebrate
retinas.

33. Adding connection holds two
possibilities
• Black box  Add connections at the level of
ganglion cells without take into account the
connection between Ganglion and Amacrine?
• Adding both GG and GA physical connections?

34. Black Box
Rods-Cones
Horizontal
Amacrine
RGC
Adding connection between RGC: These
connection take (in a hidden way) the
connections between the RGC and
Amacrine.

35. Amacrine-RGC
Rods-Cones
Horizontal
Amacrine
RGC
Adding connection between RGC: These
connection take (in a hidden way) the
connections between the RGC and
Amacrine.

38. Center Surround Antagonism
- + -
PR
B
RGC

39. http://news.softpedia.com/news/Con
nections-Between-Retinal-Cell-
Population-Mapped-159743.shtml
• “Nobody has ever seen the entire input-
output transformation performed by complete
circuits in the retina at single-cell resolution,”
explains expert E.J. Chichilnisky, PhD.
“We think these data will allow us to more
deeply understand neuronal computations in
the visual system and ultimately may help us
construct better retinal implants,” adds the
scientist.