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I have few questions about the firing rate of retinal ganglion cells.

1) How to explain the baseline firing rate if either the entire receptive field is stimulated or there is no light stimulus at all? That behaviour means that the intensity of light does not have any effect if the entire receptive field receives the same stimulus. I don’t understand how horizontal cells let that possible.

2) When the on-center is stimulated, the firing rate is maximized at the beginning and it diminishes with time to reach the baseline rate. Why does the firing rate decrease? What is responsible for that? neural activity

3) Is it possible to have a simple mathematical model of the process with an artificial neural network?

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  • $\begingroup$ It's best to limit one question per question, especially when they are not closely related (Q3 here, e.g.). $\endgroup$
    – kmm
    Commented Apr 10, 2018 at 23:08

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1) This is a bit simplified; in reality, flashes of light or dark that cover the whole receptive field do influence the firing rate somewhat, just not nearly as much as an on-center stimulus for an on-center RGC. Your textbook is using a bit of an idealized interpretation to convey the concept of center-surround organization. I'm not sure what your confusion related to the horizontal cells is, however.

2) This is usually called "adaptation" and is a general principle in nervous systems (particularly on the sensory side). Multiple systems influence adaptation, including depletion of neurotransmitter-containing vesicles, metabotropic receptors activated by high concentrations of neurotransmitter that have opposite-sign effects to ligand-gated receptors, feedback systems that suppress the potency of second-messenger systems, accumulation of extracellular inhibitory neurotransmitters, etc. For the eye, there are additional sources of adaptation that come into play, depending on the experimental paradigm.

Without knowing the exact paradigm your textbook is meaning to indicate, it's probably more important at this point to just recognize adaptation as a normal aspect of sensory processing. The specific mechanisms can be understood later.

3) Yes - but you don't need to go to anything as complex as an artificial neural network. Basic image filters like the Laplacian of Gaussian (LOG) filter are basic approximations of center-surround organization in the retina.

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  • $\begingroup$ Thank you very much for your answer! Retina horizontal cell article on Wikipedia says that horizontal cells allow eyes to see under different light conditions. So I deduced that they are responsible of the "adaptation" you are talking about. That's right? $\endgroup$
    – ardayigit
    Commented Apr 11, 2018 at 8:12
  • $\begingroup$ @ardayigit That's an incomplete explanation from Wikipedia then about the role of horizontal cells. They can have some role in adaptation, but there are many other mechanisms for adaptation and horizontal cells also have a role in making center-surround organization more robust. $\endgroup$
    – Bryan Krause ♦
    Commented Apr 11, 2018 at 16:41
  • $\begingroup$ so many cells are involved in adaptation. I can not say if it is done by photoreceptors, bipolar cells, etc. $\endgroup$
    – ardayigit
    Commented Apr 12, 2018 at 9:18

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