Prosthetic retina turns neural codes into clearer images than older methods can produce.
A new retinal prosthetic creates an image (middle) that more accurately reconstructs a baby’s face (left) than the standard approach (right).
Credit: S. Nirenberg
Normally, cells that respond to light, called photoreceptors, pick up signals and transfer that information to ganglion cells. These cells then create a complex code for each visual signal that goes into the brain, where the scene is reconstructed. Spotting a dog creates a particular code, for example, different from the code for a teacup or a baby’s face. When a retina is degenerated, these photoreceptor cells die and there is no message to send. Nirenberg’s new system mimics the complex behavior of the frontline photoreceptor cells, creating a more natural artificial message for the ganglion cells to interpret. Other prosthetics produce simpler, less recognizable codes, Nirenberg said. These simplified patterns aren’t what the brain is used to receiving, so while they can reproduce simple features, they can’t reproduce natural scenes. Because the new prosthetic speaks the language that the ganglion cells are accustomed to, the ganglion output — and the image — is more accurate.
The way the team tested their hypothesis is very clever. They decoded the output of the ganglion cells by measuring cellular activity when an image of a baby’s face was presented to the retinas of blind mice. Patterns measured from the mice with the new prosthetic reproduced a baby’s face in much finer detail than the standard method did. Instead of the standard method’s highly pixilated, blurry version of the face, the new prosthetic captured a smooth, clear view of the baby’s quizzical expression. “Not only can you tell it’s a baby’s face, you can tell it’s this baby’s face,” Nirenberg said.
The researchers are currently testing the prosthetic on primates and plan eventually to provide the technology to human patients. That would probably require gene therapy.“Obviously it’s not in humans yet,” said Victor, also of Weill Medical College. “Everyone else is working on putting the signal into humans, and now they have the signal to put in. It’s extremely exciting.”