A neural circuit that involves both rod and cone cells in the retina and is responsible for colour vision in mice is identified in a paper published in Nature this week. Colour vision is thought to rely on the comparison of signals from colour-sensitive cone cells in the mammalian retina. How this occurs in dim light has been unclear.
Markus Meister and colleagues identify and describe a new type of neuronal circuit in specific cells, known as ganglion cells, in the retina of mice. They show that this cell type has so-called ‘opponent’ responses to light of different wavelengths, enabling both rods and cones to function together and allow colour-detection even in dim moonlight. The authors explore the ecological benefits that the mice might draw from colour vision in these light conditions. They note that mice are indeed active under these luminosity conditions and suggest that this newly identified colour vision circuit may enhance the animals' nocturnal detection of conspecifics’ urine marks, which serve an important function in social communication.
The authors argue that all components necessary for the existence of this circuit are also found in the human retina. Furthermore, this circuit’s presence in the human eye could help explain specific perceptions of colour, such as the tendency to see blue colours (so-called ‘blue shift’) at low illumination levels, for example, during twilight.