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Medical Forum / General / Vision / July 2004How the retina works
Hi, Sorry for the bit of cross-posting, I've had a couple of problems working out the best place for this post. I've done quite a lot of googling to find out how the retina works in simplistic terms but to no avail. I have been working at Carver Mead's Silicon Retina in May 91's Scientific American and have worked out so far: Light hits the cones and rods, and passed on to the horizonal cells. The horizontal cells smooths or spacially averages the signal from the rods and cones, there is also some feedback to them. The rods and cones along with the horizontal cells send a signal to the bipolar cells through the triad synapse, which basically takes the difference between them. So far the effect of this basically detects edges and motion from the original image. Is this correct so far? Now I can't find much information on the amacrine and ganglion cells, except that the amacrine cells perform a similar role to the horizontal cells and the ganglion act as a conduit to the lateral geniculate in the thalamus. Could someone kindly expand on that a bit or point me to a site that can explain it in layman terms? Any help appreciated. Wil I suggest a decent med school textbook like Kandel and Schwartz. It may help you beyond a simplistic understanding. Kal > Hi, > [quoted text clipped - 32 lines] >Checked by AVG anti-virus system (http://www.grisoft.com). >Version: 6.0.712 / Virus Database: 468 - Release Date: 27/06/2004 > I suggest a decent med school textbook like Kandel and Schwartz. It > may help you beyond a simplistic understanding. > > Kal I probably should get a book like that. What I'm trying to do is make a simulation of essentially the essence of how the various layers work, and then to later build on the output of that work. I'm currently at the stage of researching whether my plans make ant sense! Basically I don't want to be spiralling off doing research on retinas at least until I know there's merit in building a simplistic model. To that end I currently need an overview of the various layers. Wil >> I suggest a decent med school textbook like Kandel and Schwartz. It >> may help you beyond a simplistic understanding. [quoted text clipped - 10 lines] >know there's merit in building a simplistic model. >To that end I currently need an overview of the various layers. In that case, what you need is far more than the introductory type things I outlined in another response. If you want your model to be anything other than simplistic, you need to understand what real neurons do, as opposed to "cartoon" neurons used in most "neural" models. These are quite fine for research in information processing, even for research in visual information or image processing. They are not at all suitable for research in how the eye actually works. You need to understand the details of signal conduction down branching dendrites, about transmitter release by graded signals, about synaptic plasticity. You need to understand the details of microcircuit anatomy of the retina. You need to understand the details of neurophysiology of the retina derived from electrophysiological studies. In short, you need to go through some hefty neuroscience text as just a start and then work your way into the primary literature. I strongly recommend Kandel, Schwartz, and Jessel, Principles of Neural Science McGraw-Hill, 2000 Squire et al. Fundamental Neuroscience, 2nd ed Academic Press 2002 Shepherd Synaptic Organization of the Brain, 5th Ed Oxford U. Press, 2003 You also must read Koch Biophysics of Computation: Information Processing in Single Neurons Oxford U Press, 1999 > In that case, what you need is far more than the introductory type > things I outlined in another response. [quoted text clipped - 5 lines] > image processing. They are not at all suitable for research in how > the eye actually works. Eeek! What I'm after is something a lot more akin to Mahowald and Mead's Silicon Retina except done in software. Would I still need to do into such detail? Wil >> In that case, what you need is far more than the introductory type >> things I outlined in another response. [quoted text clipped - 11 lines] >done in software. >Would I still need to do into such detail? That seems to be different from what you described earlier. Do you want to model the real retina or the "Silicon retina"? There is a big difference. To model the real retina, you must know really how the cells work. To model the silicon retina, all you have to know is how that works. And there, I can't help you. > That seems to be different from what you described earlier. > > Do you want to model the real retina or the "Silicon retina"? There > is a big difference. To model the real retina, you must know really > how the cells work. To model the silicon retina, all you have to know > is how that works. And there, I can't help you. You are correct, I am really after something more aligned to the silicon retina, but I also want to understand it's design in relation to a real retina and to try to understand the myriad of amacrine cells. To be honest though my research will not be going in to PhD detail! I have to say though I went though the site you suggested and it is extremely good, there is a pdf download that gives a fantastic overview of the retina and is exactly the sort of thing I was after. I also have a collection of papers about neurons on order it includes "The Functional Architecture of the Retina" in the Dec. 1986 Scientific American, though I just found out I think you can get those old papers from the sciam site, anyway definitely worth a read. All in all thanks for your responses, they have definitely helped me refine what I am looking for. Wil >> That seems to be different from what you described earlier. >> [quoted text clipped - 16 lines] > the sort of > thing I was after. So you probably already got: Helga Kolb's overview "How the Retina Works" available at: http://webvision.med.utah.edu/index.html A nice website on the evolution of the retina is: http://www.pigeon.psy.tufts.edu/avc/husband/avc4eye.htm As for the "upside down design", Stephen Palmer writes in the book "Vision Science: Photons to Phenomenology": ==== The reason for this unusual arrangement is probably that the enzymes that are needed for pigment regeneration are in the pigment epithelium, which is opaque. Because the receptor disks must be adjacent to this vital biochemical resource, they must also be at the back of the retina. ==== But then there is the head-foot molluscs retinal organization...(shrug). > I also have a collection of papers about neurons on order it includes "The > Functional [quoted text clipped - 13 lines] > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.712 / Virus Database: 468 - Release Date: 27/06/2004 > So you probably already got: > > Helga Kolb's overview "How the Retina Works" > available at: > http://webvision.med.utah.edu/index.html Yep that's the same one, it's not half bad. > A nice website on the evolution of the retina is: > > http://www.pigeon.psy.tufts.edu/avc/husband/avc4eye.htm That seems food as well, thanks! > As for the "upside down design", Stephen Palmer writes in the book "Vision > Science: Photons to Phenomenology": [quoted text clipped - 7 lines] > > But then there is the head-foot molluscs retinal organization...(shrug). Do I want to know :) ? Wil >>> I suggest a decent med school textbook like Kandel and Schwartz. It >>> may help you beyond a simplistic understanding. [quoted text clipped - 50 lines] > > FWIW, I'm not sure you need to go into each layer, so much as the effective output of the ganglion cells and center-surround antagonism. It depends on why you want to model the retina in the first place. Even more pertinent to your work might be Marr, "Vision", Freeman, 1982. In all your searches, add the phrase "lateral inhibition"-- its my favorite network architecture. It retina, it serves as a spatial differentiator, but in brainstem and spinal cord is serves a temporal integrator. Lateral inhibition-- is there anything it can't do? Scott "Scott Seidman" <namdiesttocs@mindspring.com> wrote in message > > FWIW, I'm not sure you need to go into each layer, so much as the > effective output of the ganglion cells and center-surround antagonism. [quoted text clipped - 7 lines] > > Scott Lateral inhibition looks promising I must say. It resembles a self organising map in neural networks and seems to be very useful! I'm presuming that the horizontal and amacrine cells exhibit lateral inhibition, so there's no getting away from it! Wil > "Scott Seidman" <namdiesttocs@mindspring.com> wrote in message > >> FWIW, I'm not sure you need to go into each layer, so much as the [quoted text clipped - 22 lines] > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.712 / Virus Database: 468 - Release Date: 27/06/2004 Lateral inhibition is the mechanism for the whole center-surround antagonism operation of the retina. If you think about it, it not only enhances edge detection, it increases the dynamic range of the entire retina. The horizontal cells implement lateral inhibition at the photoreceptor level, and the amacrine cells at the ganglion cell level. The bipolar cells essentially define whether a ganglion cell is on- center/off-surround, or off-center/on-surround. An interesting tidbit-- the light has to pass through the ganglion, bipolar, amacrine, and horizontal cells, as well as the cell body of the photoreceptors, before hitting the light sensitive parts of the photoreceptor. At the fovea, this isn't as true-- the upper layers are sort of pushed aside Scott > Lateral inhibition is the mechanism for the whole center-surround > antagonism operation of the retina. If you think about it, it not only > enhances edge detection, it increases the dynamic range of the entire > retina. I thought this happens thought feedback from the horizontla cells and from the photoreceptors themsleves. When this happens is it not just a relative shift in sensitivity? > An interesting tidbit-- the light has to pass through the ganglion, > bipolar, amacrine, and horizontal cells, as well as the cell body of the [quoted text clipped - 3 lines] > > Scott I picked up on the the light passing though all the layers as well, what is the relevance of this not happening at the fovea? Or to be more precise, do you know why light passes through all the layers first? Wil > I picked up on the the light passing though all the layers as well, > what is the relevance of this not happening at the fovea? > Or to be more precise, do you know why light passes through all the > layers first? > > Wil The fovea does our highest acuity work, so the most direct path for light seems to have evolved there. As for why light passes through all the other layers, noones come up with a good reason for that. Maybe it has some protective function for the receptors, maybe the retina is mechanically more stable that way, maybe its just an evolutionary quick. FWIW, I seem to recall being told that the octopus retina is not layered this way, but I can't vouch for the info Scott >> Lateral inhibition is the mechanism for the whole center-surround >> antagonism operation of the retina. If you think about it, it not only [quoted text clipped - 16 lines] >of this not happening at the fovea? >Or to be more precise, do you know why light passes through all the layers first? Lateral inhibition doesn't just change the sensitivity, it is what is primarily responsible for edge detection, contrast enhancement, etc. The center-surround organization is just another way to describe lateral inhibition. Yes, it involves connections through the horizontal cells. I don't think the retinal layers are different in the fovea -- light still does pass through all the neural cell layers. What is different is that in the rest of the retina light also has to dodge the bundles of axons and the blood vessels supplying the retina. These tend to skirt around the fovea. Why the eye is built that way is another story. One idea is that it is just an example of "incredibly stupid" design, in opposition to the "intelligent design" notion. It probably was simply a bad design "choice" early in the evolution of the vertebrate eye that was frozen in place by succeeding evolutionary steps. It certainly does work well enough, so no big deal. Cephalopod molluscs (squid and octopus) have complex camera eyes with layered retinas that are built the "right way", with the photoreceptors on the surface so they are the first cells that light hits. > I don't think the retinal layers are different in the fovea -- light > still does pass through all the neural cell layers. What is different > is that in the rest of the retina light also has to dodge the bundles > of axons and the blood vessels supplying the retina. These tend to > skirt around the fovea. At the fovea, the bipolar cells go off at an angle insted of coming straight off from the receptor, essentially getting out of the way. Kandel and Schwarz have a pretty good picture of it Scott > I don't think the retinal layers are different in the fovea -- light > still does pass through all the neural cell layers. What is different [quoted text clipped - 11 lines] > "right way", with the photoreceptors on the surface so they are the > first cells that light hits. It would seem odd that light has to pass thought all the other layers first, you would imagine that light is being muted going thought those other layers. Seeing as we a so extremely dependant on sight this would be a very evolutionary big disadvantage. > It would seem odd that light has to pass thought all the other layers > first, you would imagine that light is being muted going thought those > other layers. Seeing as we a so extremely dependant on sight this > would be a very evolutionary big disadvantage. Hasn't done us in yet! Scott > I don't think the retinal layers are different in the fovea -- light > still does pass through all the neural cell layers. What is different > is that in the rest of the retina light also has to dodge the bundles > of axons and the blood vessels supplying the retina. These tend to > skirt around the fovea. A cross-section micrograph shows the retina _does_ thin significantly at the fovea, forming a concave pit that produces the "foveal light reflex" seen with the ophthalmoscope. IIRC the cross-section shows thinning in the two nuclear layers, fewer cell bodies, as well as fewer axons. Fewer axons The axons are transparent. And actually, the blood vessels are pretty transparent too. When you see vessels with an ophthalmoscope, you're seeing the "blood column," not the vessel walls. The blood column is essentially opaque, and casts a distinct shadow. If it were a simple camera, the film would have a superimposed blood-vessel pattern on every picture. Instead, the retina "filters out" static images, those without moving edges. If you wiggle a penlight against the sclera and cause the shadows to move, the vessels become dramatically visible - a phenomenon called Purkinje's tree. -MT > The blood column is essentially opaque, and casts a distinct shadow. If it > were a simple camera, the film would have a superimposed blood-vessel > pattern on every picture. Instead, the retina "filters out" static images, > those without moving edges. If you wiggle a penlight against the sclera and > cause the shadows to move, the vessels become dramatically visible - a > phenomenon called Purkinje's tree. I was under the impression that the brain compensated for the vascular shadows on the retina. Hence the "representation", so to speak, of the vessels in cortex (eg. Horton's recent "angioscotoma" papers). > Lateral inhibition looks promising I must say. It resembles a self organising map in > neural networks and seems to be very useful! > I'm presuming that the horizontal and amacrine cells exhibit lateral inhibition, so > there's no getting away from it! It may be worthwhile to start with Hartline's work on limulus and advance into the many subsequent modelling (etc) papers. Passaglia and Barlow '98 is an interesting one. Relevance to mammalian retina? Sure, why not? >> I suggest a decent med school textbook like Kandel and Schwartz. It >> may help you beyond a simplistic understanding. [quoted text clipped - 10 lines] >know there's merit in building a simplistic model. >To that end I currently need an overview of the various layers. I think you need more than an overview; you need an intimate understanding of the processing of each of the interacting components. By this, I mean that a 'simplistic' definition by cell or by layer will not permit you to design a useful model. Kal >Wil > >--- >Outgoing mail is certified Virus Free. >Checked by AVG anti-virus system (http://www.grisoft.com). >Version: 6.0.712 / Virus Database: 468 - Release Date: 27/06/2004 > I think you need more than an overview; you need an intimate > understanding of the processing of each of the interacting components. > By this, I mean that a 'simplistic' definition by cell or by layer > will not permit you to design a useful model. I think you could be right, it might be time to have a rethink! Wil > I'm currently at the stage of researching whether my plans make ant sense! > Basically I don't want to be spiralling off doing research on retinas at least until I > know there's merit in building a simplistic model. > To that end I currently need an overview of the various layers. It would be useful to review research into the various "entoptic" phenomena like afterimages, color persistence, and edge detection, as well as comparative animal physiology. Simpler models are preferred, as long as they explain the observed phenomena. -MT > > I'm currently at the stage of researching whether my plans make ant sense! > > Basically I don't want to be spiralling off doing research on retinas at [quoted text clipped - 10 lines] > > -MT That is exactly what I am trying to model, I have more of an interest in edge detection than in the make up of the retina in a physiological sense. Do you know of any models I could look at? Wil >> > I'm currently at the stage of researching whether my plans make ant >> > sense! Basically I don't want to be spiralling off doing research [quoted text clipped - 24 lines] > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.712 / Virus Database: 468 - Release Date: 27/06/2004 Definately pick up "Vision" by Marr. He uses "primitives" available at the ganglion cell layer, and arranges them to detect more features, like edges. Good stuff. Scott > Definately pick up "Vision" by Marr. He uses "primitives" available at > the ganglion cell layer, and arranges them to detect more features, like > edges. Good stuff. > > Scott From who I've seen from the Silicon Retina this already happens in the horizontal layer, I was guessing that ganglions refines what has been found. Is this possible? Wil > That is exactly what I am trying to model, I have more of an interest in edge detection > than in the make up of the retina in a physiological sense. > > Do you know of any models I could look at? As I've mentioned elsewhere in the thread, you may be better off looking at the work done in limulus in this regard. > Hi, > [quoted text clipped - 23 lines] > Could someone kindly expand on that a bit or point me to a site that can explain it in >layman terms? What you really need is a book like "The Retina: An Approachable Part of the Brain" by John Dowling, Harvard U Press, 1987. That work is, in fact, referenced in Mahowald and Mead's "Silicon Retina" paper. (Incidentally, it is not polite to ignore coauthors when citing work!" R. Masland has a brief introduction to "The Functional Architecture of the Retina" in the Dec. 1986 Scientific American. Just about every book you can find on neurobiology or neurophysiology or neuroscience or physiological psychology should have a large section, perhaps a whole chapter, on retinal information processing. these books are really essential to get a firm understanding of the anatomy and physiology behind the information processing. This seems to be a nice web site on the retina http://retina.umh.es/Webvision/ > What you really need is a book like "The Retina: An Approachable Part > of the Brain" by John Dowling, Harvard U Press, 1987. That work is, > in fact, referenced in Mahowald and Mead's "Silicon Retina" paper. > (Incidentally, it is not polite to ignore coauthors when citing work!" *blush* sorry, was being lazy! > R. Masland has a brief introduction to "The Functional Architecture of > the Retina" in the Dec. 1986 Scientific American. [quoted text clipped - 7 lines] > This seems to be a nice web site on the retina > http://retina.umh.es/Webvision/ Thanks for the leads, off down to the library for me then! Wil |
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