11 October 2011
by Ferris Jabr
Stand up too quickly and you might see stars. Analysing the area of the brain that creates these tiny flashes of light could help blind people to see.
If certain areas of the brain that process visual information are activated – by a blow to the head, for example – tiny stars of light appear in vision. People experience such “phosphenes” even if their eyes are closed or they are blind.Peter Schiller of the Massachusetts Institute of Technology in Cambridge and his colleagues stimulated these brain areas in monkeys to determine what the phosphenes look like to them and where they appear in line of sight.
First, they trained rhesus macaques to stare at two dots on a computer screen and direct their gaze towards the larger dot or the dot of higher contrast to the background. Schiller then implanted electrodes in each monkey’s primary visual cortex (V1), the main region responsible for processing visual information.
Schiller then removed one of the two dots on the computer screen and replaced it with a phosphene by stimulating an area of the V1. If the monkey’s gaze moved towards the phosphene, Schiller knew the star must be larger or of higher contrast than his programmed dot.
By varying the size of the dot on the screen, as well as the darkness and colour of the background, Schiller worked out that the stars were between 9 to 26 arc minutes (1 arc minute is 1/60th of a degree) in diameter and appeared in a variety of colours, including pink, blue, green and yellow.
“We want to understand the brain to help the blind,” Schiller says. His goal is to pair electrical stimulation of the visual cortex with a small camera – this would allow researchers to stimulate the visual cortex with a pattern of activity that translates the information captured by the camera, giving a kind of sight to blind people.
“There is growing interest in developing and applying brain-machine interfaces and neural prostheses, but there is not a whole lot of foundation in terms of understanding the coupling of physical signals you put into the brain and perceptual experiences you get out of the brain,” says John Maunsell of Harvard Medical School. “Studies like this allow you to move forward. Imagine if you could give vision back to people who have lost function of their eyes but have a perfectly intact brain.”