Several types of sight-boosting prostheses are currently under development, with some already being tested in humans. But while these largely target the retina, the Harvard researchers chose to focus on part of the visual system called the lateral geniculate nucleus (LGN), a relay station along the route from the optic nerve to the visual cortex, where visual information is processed. Because it's upstream of the eye, this area could be targeted in people with extensive eye damage.
And unlike locations in the visual cortex, the LGN is one of the first "stops" in the visual system, meaning that the neural signals encoding visual information have not yet been extensively processed and spread throughout the brain. "[In the LGN] there is a straightforward mapping of the visual scene on the tissue," says John Pezaris, a neural-systems engineer at Harvard Medical School, who led the research. This means that specific parts of the LGN are linked to specific parts of the visual scene. When a light flashes in one location, for example, the corresponding area in the LGN will become active.
