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Color-deficient persons lack the cells in their retina needed for differentiating some (or all) colors.

However, the part of the brain that actually processes images is not deficient.

Is it possible to somehow make a color-deficient person "see" the missing colors by directly activating that part of the brain responsible for processing colors?

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@RoryM I would use "vision" instead of "sight" here? Do you agree? –  Alexander Galkin Jan 13 '12 at 13:15
    
@AlexanderGalkin Yes that would be more accurate. As that tag also fits the other question I'll re-tag that too so that the tag persists after a month =) –  Rory M Jan 14 '12 at 16:57
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2 Answers

up vote 8 down vote accepted

It is a very interesting question and I did some efforts to investigate the literature on this topic, but yet I don't have a definitive answer for you. But let's start from the beginning.

First of all, the reason for color deficiency can be not only lack (rare) or impairment (more often) of certain types of color-perceiving cells (cones) in retina, but also brain injures: the central color blindness can develop after head trauma or as a result of some neurodegenerative deceases, like Parkinson's decease. In case of brain origin of the color blindness it is usually the complete color blindness (no color is percieved), whereas congenical primary color blindness (receptor-based) is usually just the unability to distinguish one or two colors, whereas the rest can be more or less separated.

I searched Pubmed for the literature on the topic and found a recent PNAS paper about the simulation of primary and secondary visual cortex on humans using intracranial electrodes. As they describe their results (bold font by me):

When percepts were elicited from late areas, subjects reported that they were simple shapes and colors....

But the paper investigated only healthy humans, no color impaired subjects were used for the tests, so cannot conclude from here whether we can elicit the perception of the color the person is incapable to see with the eyes using these stimulations.

I took this paper as the starting point and did some reference research, looking for the paper referenced there and for newer publications referencing this one: PNAS is one of the top journals in this area with very high impact factor and if there were a publication about brain stimulation and color blindness I would have definitely identified it.

During my investigations I came accross a series of interesting articles devoted to "cortical visual neuroprosthesis for the blind" (read this paper<1> from 2005 for review on this topic), but this is the treatment of conventional blindness, not the color blindness. There was no intersection in keywords or titles for color blindness and brain stimulation, both in the referenced articles and in the complete article database.

So, I would suggest that you address some talented experimentalist with your question and maybe one day, who knows, we will read your name under the Nature article dedicated to the novel way to cure color blindness.


<1> -- unfortunately not available publicly for free, I am sorry.

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Yes! And no. But first, some background.

Your central nervous system has (or is believed to have, as do other primates) a number of different organizational structures. Cells within a column (the cortex is composed of about 7 layers, and a column would be a vertical group of neurons from these layers) respond to stimuli with similar features. There are also higher order structures of collections of columns, such as orientation pinwheels(1) orientation pinwheel

Note that in the above picture, color is used to indicate orientation and not what color the column responds to. Color sensitivity itself is (as far as I'm up to date on things) simply known to occur in color opponency columns, see this paper by T'So(2) where for instance red and green color opponent columns would be found together more often than not.

The key point to take away from that is that your cortex has to develop these columns. Without them you wouldn't have normal color vision, even if you circumvented the retina and LGN entirely.

That brings us to the "Yes!" part of my answer. If you've got a person that lost their color vision late in life, they should have relatively developed color columns in their visual cortex and assuming that we could wire to those areas in a meaningful way, in sufficient resolution, and could manipulate their voltages in a directed manner (we can't) then they certainly should be able to see in color with direct cortical stimulation.

However if someone was born without color vision, I do not believe this would be possible. Not without more work than simply sending a signal in, since there is strong evidence(3) that development of the columnar organization of V1 requires visual input during later stages of development. I have read some cases where they took people with very simple retinal diseases (photoreceptor loss) and attempted to restore their vision. There was an extremely strong positive correlation between how old the patient was when they lost vision and the degree to which any sight could be restored.

References:

  1. Ohki K, Chung S, Kara P, Hübener M, Bonhoeffer T, Reid RC. 2006. Highly ordered arrangement of single neurons in orientation pinwheels. Nature 442: 925–8.
  2. Ts’o DY, Gilbert CD. 1988. The organization of chromatic and spatial interactions in the primate striate cortex. The Journal of neuroscience : the official journal of the Society for Neuroscience 8: 1712–27. [pdf]
  3. Swindale NV. 1981. Absence of ocular dominance patches in dark-reared cats. Nature 290: 332–333.
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