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If we have a spot of light hitting the center of the ON center receptive field of a retinal ganglion cell, will the LGN neuron be activated? Will the V1 neuron be activated? I mean its receptive field looks different, see the image below. I am just so confused on what the receptive field of an LGN and V1 neuron even means. In other words, how is the receptive field of the retinal ganglion cell related to or how does it affect the receptive field of the LGN neuron?

If light shines in the center of the ON center LGN neuron receptive field that is not in the receptive field of the ganglion cell, then the LGN neuron is activated and the ganglion cell is not. How does that work? How can it skip a stage? Does not the RGC first need to get activated for the LGN neuron to get activated?

Since a V1 neuron to get activated for example needs a shine of light that is 45 degrees diagonal to the right, will it get activated if only a spot of light is shone to the ON of the ON center retinal ganglion cell? This RGC is connected to the V1 neuron is it not?

In conclusion, I think that I am confused in why is the ganglion cell connected to the LGN cell, which is connected to the V1 cell, when they all have different receptive field. What does the connection bring about?

Thanks sm in advance!

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The picture is showing you how receptive fields are combined at different levels of the visual processing hierarchy. The activity of multiple cells is combined to influence the activity of the downstream cell. This diagram is a bit confusing in that it focuses only on one RGC to show divergence (connection from one to many from the RGC) from RGC to LGN and then only convergence (connection from many to one in V1).

Light doesn't only shine "on the receptive field of a retinal ganglion cell"; light shines on some spot on the retina, which will influence multiple retinal ganglion cells. If you want to understand what happens at the level of LGN or V1, you need to consider all of the inputs to a cell, not just one of them.

If we have a spot of light hitting the center of the ON center receptive field of a retinal ganglion cell, will the LGN neuron be activated?

Maybe? Who knows. Neurons in the LGN will be activated (fire action potentials) if they receive enough excitatory input (and little enough inhibitory input). If you have an ON-center RGC that synapses on an LGN cell, then yes, light at the center of the RGC receptive field will increase the likelihood that the LGN cell fires.

Will the V1 neuron be activated?

Maybe? Who knows. If light only lands on the center of one of the LGN cell receptive fields, it's also landing in the "surround" of the other adjacent LGN cells that also give input to V1. You'd expect the V1 neuron to be more active in response to a spot of light than if light only fell in the dark surround area, but far less active in response to a spot of light than to a bar/line of light that looks like the shape on the right hand side.

I would recommend working back the other way. Look at the way the receptive field is drawn: that tells you how light in different areas will influence that cell's firing. Light on the white background areas increases firing, light on the shaded areas decreases firing. Then, work backwards in the pathway to understand how those responses could have been created by adding together cells at the previous level of the processing hierarchy.

What does the connection bring about?

No light shines on any cells in the LGN or V1. These are deep in the brain. Light information needs to be transmitted to them in some way. Without connections between these cells, there would be no responses to light in the brain.

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  • $\begingroup$ Whoa! Thank you so so much! So nice of you to spend so much time answering my questions to help me out, I greatly appreciate it $\endgroup$
    – Maria
    Commented Sep 25, 2023 at 19:12
  • $\begingroup$ there is only one ganglion cell connected to only one LGN cell? But more than one LGN cells connected to a V1 cell? Does the receptive field of a ganglion cell superimpose with the receptive field of the LGN cell to which it is connected? Are their receptive fields identical? If not, lets say if that of the LGN is bigger and light is shone on a part that does not shine on the receptive field of the RGC, then how is the LGN cell activated when RGC is not? Since only this RGC is connected to that LGN cell so it is the only one that can activate the LGN cell (?) $\endgroup$
    – Maria
    Commented Sep 25, 2023 at 19:35
  • $\begingroup$ and since V1 cells are only activated by bars of light, then if I am seeing a round spot of light, is any of my V1 neurons being activated? $\endgroup$
    – Maria
    Commented Sep 25, 2023 at 19:45
  • $\begingroup$ @Maria Each RGC connects to multiple LGN cells; each LGN cells receives input from multiple RGCs. Each LGN cell connects to multiple V1 cells, and each V1 cell receives input from multiple LGN cells. There are also lots of different types of V1 cells and receptive fields, arranged in different layers of cortex; only the "simple cell" is being depicted here. $\endgroup$
    – Bryan Krause ♦
    Commented Sep 25, 2023 at 19:45
  • $\begingroup$ V1 cells are activated best by bars of light. How V1 will be activated will depend on the size of the spot of light; if it's small then yes, any V1 cells where that spot would fall on their 'bar' would be weakly activated. If it's a big circular spot of light, you'd expect V1 cells to be activated in a pattern consistent with a line of "bars" along the edge of the circle in a tangent orientation, where light lands on their center and one side of the surround, but not the other side. V1 receptive fields are also considered "edge detecting". $\endgroup$
    – Bryan Krause ♦
    Commented Sep 25, 2023 at 19:48

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