Cells measure brightness to see the light
08 December 2010
University of Manchester researchers Professor Rob Lucas and Dr Tim Brown hope that their findings from studies in mice will lead to a new understanding of how we perceive the world and, eventually, might lead to technical applications in artificial lighting, visual display unit and television screen design.
Signals from the rod and cone cells in the eyes send information on movement, shape and colour to the brain via neurons that form the optic nerve. The Manchester team has found that 2 per cent of these neurons produce a light-sensitive protein known as melanopsin and play an integral part in measuring the brightness of the world around us.
It was previously thought that these melanopsin cells were responsible for detecting light for subconscious responses to light, such as changing pupil size. However, the team found that melanopsin also helped regions of the brain involved in conscious perception to measure brightness, not only in normally sighted mice but also in those previously considered to be blind.
Dr Brown, from Manchester's Faculty of Life Sciences, said: "This reveals a new role for melanopsin in perceiving brightness and suggests that these cells could support vision even in people with advanced retinal degeneration.
"Loss of rods and cones is a common cause of blindness, but people suffering these conditions often retain some light perception. The accepted explanation for such cases has been that they reflect incomplete rod and cone loss. We have shown that in mice with similar conditions, light responses can in fact rely on melanopsin."
Professor Lucas added: "Now we are asking to what extent melanopsin could help the normally sighted to see, and what it might contribute to the blind and partially sighted.
"So far, our results suggest that we rely upon melanopsin to perceive the difference in brightness between a foggy day in London and bright summer sunshine in Manchester. We need to know whether it also provides the spatial information we rely upon for more complex sorts of vision.
"Our findings could change the way that we think about artificial lighting and may even improve the ability of computer displays or televisions to reproduce our perception of the real world. At the moment both of these technologies are designed only with rod and cone cells in mind."
The study, in which Professor Lucas and Dr Brown collaborated with researchers at the Salk Institute in San Diego and University College London's Institute of Ophthalmology, is published this week in 'PLoS Biology'.
Image: Michele Catania on Flickr.
Reference
Brown TM et al. Melanopsin contributions to irradiance coding in the thalamo-cortical visual system. PLoS Biol 2010 [Epub ahead of print].
