Bionic vision: Bypassing the eyes

The quest to restore sight by sending electrical signals directly to the brain

Scientists are a step closer to restoring vision for the blind, after building an implant that bypasses the eyes and allows monkeys to perceive artificially induced patterns in their brains. The technology, developed by a team at the Netherlands Institute for Neuroscience (NIN), was described in the journal Science.

The concept builds on an idea first conceived decades ago: electrically stimulating the brain so it “sees” lit dots known as phosphenes, akin to pixels on a computer screen. But the concept had never realized its full potential because of technical limitations.

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Visual cortex

A team led by NIN director Pieter Roelfsema developed implants consisting of 1,024 electrodes wired into the visual cortex of two sighted monkeys, resulting in a much higher resolution than has previously been achieved. The visual cortex is located at the back of the brain and many of its features are common to humans and other primates.

This allowed the pair of monkeys to make out shapes like letters of the alphabet, lines and moving dots, which they’d previously been trained to respond to by moving their eyes in a particular direction to win a reward.

The NIN team benefited from advances in miniaturization, and also devised a system to make sure their input currents were big enough to create noticeable dots, but not so great that the pixels grew too large.

They achieved this by placing some electrodes at a more advanced stage of the visual cortex, to monitor how much signal was coming through and then adjust the input.

Wireless future

Roelfsema said his team hopes to make similar devices for humans in about three years. But the electrodes the team used require silicon needles that work for about a year before tissue builds up around the needles and they no longer function.

Ultimately, a wireless solution would be best, as it would mean the user wouldn’t need to wear an implant on the back of their skull, which requires scientists to operate and puts the user at risk of infection.

Fortunately, wireless devices that interface with the brain are advancing rapidly. The prosthetics would only be suitable for people who once had sight and then lost it owing to disease or injury.
The brains of people who are born blind dedicate the visual cortex to other functions. But in people whose eyes stop working, the brain region remains idle, waiting for an input that never comes.

Bionic vision

Light enters the eye through the lens and hits the retina, which turns it into electrical signals

We see when the signals arrive at the visual cortex in the brain via the optic nerve

Instead of restoring sight through the eyes, one approach aims to stimulate vision directly via implants in the brain

Electrical stimulation of the visual cortex can reliably create the perception of a brief, bright flash of light, known as a phosphine

A camera would capture the view of what the subject is “looking at” and the signal will be processed and sent directly to the brain

It is hoped that the use of high definition intracortical electrodes will one day improve resolution enough to make functional vision viable through this system.

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