Visual neurobiology: Colouring the cortex

In humans, the neural basis for colour vision lies in the activity of the 'colour-opponent' neurons, which receive inputs of opposite sign from the three different classes of cone photoreceptors that are found in the eye (Fig. 1). Colour-opponent neurons are abundant in the first stages of the visual pathway — the retina and the lateral geniculate nucleus. Surprisingly, however, they are observed rather infrequently by single-cell recordings in the next stage, the primary visual cortex (V1), where neurons that add inputs from all three cone types predominate