Tuesday, June 30, 2009

Color vision, cones, and color-coding in the cortex.

Conway BR.
Neuroscientist. 2009 Jun;15(3):274-90.

Color processing begins with the absorption of light by cone photoreceptors, and progresses through a series of hierarchical stages: Retinal signals carrying color information are transmitted through the lateral geniculate nucleus of the thalamus (LGN) up to the primary visual cortex (V1). From V1, the signals are processed by the second visual area (V2); then by cells located in subcompartments ("globs") within the posterior inferior temporal (PIT) cortex, a brain region that encompasses area V4 and brain regions immediately anterior to V4. Color signals are then processed by regions deep within the inferior temporal (IT) cortex including area TE. As a heuristic, one can consider each of these stages to be involved in constructing a distinct aspect of the color percept. The three cone types are the basis for trichromacy; retinal ganglion cells that respond in an opponent fashion to activation of different cone classes are the basis for color opponency (these "cone-opponent" cells increase their firing rate above baseline to activation of one cone class and decrease their firing rate below baseline to activation of a different cone class); double-opponent neurons in the V1 generate local color contrast and are the building blocks for color constancy; glob cells elaborate the perception of hue; and IT integrates color perception in the context of behavior. Finally, though nothing is known, these signals presumably interface with motor programs and emotional centers of the brain to mediate the widely acknowledged emotional salience of color.

PMID: 19436076

1 comment:

brain - research neuroscience group said...

I liked your article! Very concise! I find fascinating that we have neurons for colors that are tuned for a huge range of hues,each neuron with a limited prefference in the color space. So neurons in the cortex are not tuned just for the 2 main opposite axis of colors - red-green, yellow-blue as in the retinal or LGN neurons. Also it is possible to have more neurons for intermediate hues because in nature this intermediate hues are more frequently present. The color tuned neurons can change their color prefference whith some degree depending on the color of the

background or in relation with the dominant color an so on... This color tuned neurons are

permanently modulated by attention, novelty discovering mechanisms, and under the pressure of

habituation and many other factors. If they have modulatory effect on other neuronal population (wich is almost obvious), it is astonishing how many new computations are inserted in the vision and visual perception proccess by just one aspect of the color vision. Also see http://neuroscience-bucharest.blogspot.com/2009/08/color-of-neurons-or-color-of-success.html