The human retina allows the eye to follow the path of a moving object, such as a Ping-Pong ball in play. Neuroscientists have been toiling for 50 years to explain how, but they lack the processing power to map the eye’s neural network. (With today’s cutting-edge modeling software, 100 people would have to work 24/7 for half a million years.)

An online game called EyeWire, developed at MIT, harnesses the power of gamers instead. Each player navigates a single nerve’s path across a tiny section of mouse retina. “It’s actually extremely challenging,” says Amy Robinson, EyeWire’s creative director. “No computer program can do it automatically.”

Some 135,000 gamers have spent a year and a half connecting retinal dots, which scientists then used to reconstruct the neural wiring in 3-D and hypothesize how the retina processes observed motion. They published their findings in Nature in May.

Now the team is working on a game that traces nerves in the olfactory cortex to find out how the brain associates emotions with particular smells.

This article originally appeared in the September 2014 issue of Popular Science.