The Guardian has a great article about how scientists are using gamers to solve the mystery of retinal motion detection.
A large group of gamers, working with computational neuroscientists, has produced a wiring diagram of the nerve cell connections at the back of the eye, which may have solved the long-standing question of how cells in the retina detect motion.
50 years ago, researchers discovered that retinal ganglion cells, which transmit information from eye to brain via the optic nerve, are sensitive to the direction and speed of moving images, and have been trying explain how ever since. The new diagram, published today in the journal Nature, points to an elegant ‘space-time wiring’ mechanism that makes a certain type of cell sensitive to motion in very specific directions.
Light entering the eye falls on photoreceptors, which convert it into electrical impulses and then transmit the information to bipolar cells. The information then passes to neurons called starburst amacrine cells, and then is transmitted to the retinal ganglion cells, which relay it to the visual cortex at the back of the brain.
The secret of how the retina detects motion seems to lie in the starburst amacrine cells (above), and the connections they form with the bipolar neurons. Starburst amacrine cells are flat with an elaborate array of extremely fine, branched dendrites. Each acts as a computational unit in its own right, and is sensitive to visual stimuli that move away from the centre of the cell out towards the tip of the branch. Earlier research has also shown that some bipolar neurons respond to visual stimuli more slowly than others.
Both starburst amacrine cells and bipolar neurons come in various different types, but the arrangement of connections between them was not know in any great detail. Jinseop Kim of the Massachusetts Institute of Technology and his colleagues reasoned that the pattern of connections between them might reveal something about how the starburst amacrine cells detect motion, and so decided to map them.
The researchers collected a series of electron microscope images of the mouse retina and partly reconstructed them into a large series of ‘cubes,’ each comprising about 17 Megabytes of data, and representing a tiny three-dimensional chunk of retinal tissue about 5 microns (thousandths of a millimetre) across. They then handed the cubes over to members of EyeWire, an online community of more than 100,000 gamers. The information was distributed via CloudFront, Amazon’s content distribution network, which cached the cubes in servers around the world so that they could be delivered to the ‘EyeWirers’ quickly.
“2,183 people from the EyeWire community helped us to reconstruct the starburst amacrine cells,” explains senior author Sebastian Seung, now at Princeton University, adding that only elite members of the online community were involved. “They had to pass the Starburst Challenge. They got a sequence of cubes, and for each one they had to reconstruct part of the branch of an amacrine cell. They had to do a certain number of cubes in a row with a certain degree of accuracy to pass the challenge, and those who qualified could go on to unlock the starburst cells.”
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