Spring 1995 Volume 4, Number 2
In brain research, as in poetry, eyes are a world of mystery and challenge. How does the eye translate a constant flood of input from the world into information useful to cognitive areas of the brain? Markus Meister and his colleagues at Harvard University are trying to find out by studying retinal ganglion cells, the output neurons of the retina. Light from objects in the environment activates the photoreceptor cells, and subsequent layers of retinal neurons begin to process this raw neural image. The result is sent to the brain by the ganglion cells, in the form of tiny electrical pulses, streaming along the fibers of the optic nerve, which form the basis of all our visual experience.
Until recently, the rules by which these signals define what may be seen had been studied only for one cell at a time. Meister's team is working to penetrate the neural code of the entire neural population, using an electrode array capable of monitoring up to 100 cells at a time. From work with salamanders, mice, ferrets, and rabbits, it is now apparent that the optic nerve fibers engage in patterns of concerted neuronal activity that were unexpected on the basis of earlier analysis. These modes of synchronous firing will significantly alter our understanding of how the eye encodes the visual environment. Moreover, they are thought to play an important part in the development of the visual system during early life, by guiding the formation of proper connections within the brain.
