Talk:Receptive field

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Delldot - Is the diagram here correct?

You state that the when both the center and the surround are dark, both the on center cell and the off center cell do not fire. If I'm understanding receptive fields correctly (which is a pretty damn hard thing to do), I would think the off center cell would fire under these conditions for two reasons:

1. A photoreceptor can either depolarized or hyperpolarized (release or not release glutamate), which leads to opposite reactions in ON and OFF cells [(glutamate --> ON cell inhibited / OFF cell excited) OR (no glutamate --> ON cell excited / OFF cell inhibited)]. So if the ON cell is inhibited in the dark center/surround scenario, wouldn't the OFF cell be excited?

2. The OFF cell is naturally excited by dark current, and there is nothing to inhibit this response

A. The OFF cell's photoreceptor is depolarized in the dark --> 
   PR releaes glutamate --> 
   OFF cell is excited (depolarized)
B. Horizontal cells from adjacent photoreceptors are also depolarized --> 
   H1 cells are depolarized --> PR synaptic cleft is depolarized --> 
   does not affect the release of glutamate from PR (since PR depolarization is already causing neurotransmitter to be released) --> 
   OFF cell remains excited

[edit] Definitions

I'm confused about the two definitions in the first two paragraphs. In most cases they don't refer to the same thing, right?