Does the brain play a part in Magno and Parvo channel creation

  • Thread starter sazr
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Main Question or Discussion Point

Regarding human vision and the retina:
The retina model presents two outputs that benefit from the above cited behaviors.
  • The first one is called the Parvocellular channel. It is mainly active in the foveal retina area (high resolution central vision with color sensitive photo-receptors), its aim is to provide accurate color vision for visual details remaining static on the retina. On the other hand objects moving on the retina projection are blurred.
  • The second well known channel is the Magnocellular channel. It is mainly active in the retina peripheral vision and send signals related to change events (motion, transient events, etc.). These outing signals also help visual system to focus/center retina on 'transient'/moving areas for more detailed analysis thus improving visual scene context and object classification.
Where are these channels produced? To put it simply, is it produced in the eye or in the brain. For example; does light enter the eye, hits the retina and it applies a series of filters to produce these 2 different channels (the parvo and magno) and it outputs this information to the brain via the optic nerve? Or does light enter the eye, hits the retina and it applies a series of filters, it excites certain ganglion cells that fire, those signals are grouped and output to the brain via the optic nerve and the brain is then responsible for converting this information into 2 channels; the parvo and magno?
 

Answers and Replies

BillTre
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Yoou should provide more information about these two channels. I am not familiar with te terminology. Parvacellular and magnocellular will usually refer to small (parvo-) or large (magno-) cells. Where exactly this terminology is referring to large or small cells is unclear.
Nevertheless, here is a guess:
The retina has different cells in different areas (as you already noted). The output cells from the retina are the ganglion cells. They can be large or small.
It would make sense that the ganglion cells in and near the retina would be small in order to generate a spatially detailed output. The spread of the the ganglion cell dendrites would get input for a more restricted area of the retina, and therefore provide information to the brain from a smaller region of the visual field.
The peripheral retina has gangliion cells with larger dendritic spreads. They can get input from larger areas of the visual field. This would be useful in detecting motion which could involve larger areas of the visual field.
These different kinds of ganglion cells can then project to different brain areas where their different kinds of information would be useful.
In this case the two channels might correspond to the different kinds of ganglion cell axons going to different brain areas.
There are a large variety of different ganglion (and other) cells in the retina which can react to different features of the visual field. There are also several neurons (bipolar, horizontal, amacrine) in the retina that can affect theh neural signal before it gets to the ganglion cells. In addition, these different kinds of cells can be found in different areas of the retina.
 
atyy
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The M and P pathways largely inherit their different properties from different types of retinal neurons, ie. the channels originate in the retina.

https://www.cns.nyu.edu/~david/courses/perception/lecturenotes/V1/lgn-V1.html
"The top four are parvocellular layers, two layers from each eye. Parvo (small) LGN cells receive inputs from (small) midget ganglion cells.
The bottom two are magnocellular layers, one layer from each eye. Magno (large) LGN cells receive inputs from (large) parasol ganglion cells."

https://nba.uth.tmc.edu/neuroscience/m/s2/chapter15.html"The neurons in the magnocellular layers (mLGN cells)
process M-retinal ganglion cell inputs
behave like M-retinal ganglion cells
...
The neurons in the parvocellular layers (pLGN cells)
process P-retinal ganglion cell inputs
behave like P-retinal ganglion cells"
 

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