Shapes revealed with stimulation of visual cortex

For many adults, blindness often results from damage to the eyes or optic nerve while the brain remains intact. This has prompted researchers to investigate devices that could restore sight by bypassing damaged eyes and delivering visual information from a camera directly to the brain.

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In a paper published in Cell, researchers at Baylor College of Medicine in Houston describe an approach in which implanted electrodes are stimulated in a dynamic sequence, essentially ‘tracing’ shapes on the surface of the visual cortex that participants were able to ‘see’.

"When we used electrical stimulation to dynamically trace letters directly on patients' brains, they were able to 'see' the intended letter shapes and could correctly identify different letters," senior author Daniel Yoshor said in a statement. "They described seeing glowing spots or lines forming the letters, like skywriting."

Earlier methods to stimulate the visual cortex treated each electrode like a pixel in a visual display, stimulating many of them simultaneously. Participants could detect spots of light but found it hard to discern visual objects or forms.

"Rather than trying to build shapes from multiple spots of light, we traced outlines," said first author Michael Beauchamp. "Our inspiration for this was the idea of tracing a letter in the palm of someone's hand."

The team tested the approach in four sighted people who had electrodes implanted in their brains to monitor epilepsy and two blind people with electrodes implanted over their visual cortex as part of a study of a visual cortical prosthetic device. Stimulation of multiple electrodes in sequences produced perceptions of shapes that subjects were able to correctly identify as specific letters.

The researchers said the approach demonstrates that it could be possible for blind people to regain the ability to detect and recognise visual forms by using technology that inputs visual information directly into the brain. The researchers caution that several challenges must be overcome before this technology could be implemented in clinical practice.

"The primary visual cortex, where the electrodes were implanted, contains half a billion neurons. In this study we stimulated only a small fraction of these neurons with a handful of electrodes," Beauchamp said. "An important next step will be to work with neuroengineers to develop electrode arrays with thousands of electrodes, allowing us to stimulate more precisely. Together with new hardware, improved stimulation algorithms will help realise the dream of delivering useful visual information to blind people."