New Stimulation Approach Produces 'Form Vision' in Blind People

By Will Boggs MD

May 20, 2020

NEW YORK (Reuters Health) - A new approach that involves dynamic stimulation of the visual cortex can allow blind people to recognize various letter shapes, researchers report.

In early testing of visual cortical prostheses (VCP), stimulation of multiple cortical electrodes produced only percepts of multiple small flashes of light (known as phosphenes) that did not combine into recognition of coherent forms.

Dr. Daniel Yoshor from Baylor College of Medicine, in Houston, Texas, and colleagues sought to overcome this obstacle by developing an alternative approach using dynamic activation of a sequence of electrodes, an approach analogous to tracing letters on the palm.

By passing a current through two adjacent electrodes, a virtual electrode is created midway between them, a technique known as current steering, the researchers explain in Cell.

When the current was varied dynamically on a rapid timescale and combined with current steering, a sighted participant was able to easily reproduce each of four letters with an accuracy of 66%.

The same approach in one blind participant resulted in correct identification of 14 out of 15 patterns (93% correct vs. 20% chance rate) and in another blind participant resulted in correct identification of 37 out of 40 patterns (93% vs. chance rate of 25%), both significant findings.

In further experiments, one participant correctly identified 26 of 30 forms (87% correct vs. chance rate of 50%) when they were delivered at the rate of 86 forms per minute and 33 of 36 forms (92% correct vs. a chance rate of 33%) when they were delivered at the rate of 30 forms per minute.

Across sighted and blind participants, dynamic stimulation and dynamic current steering stimulation produced percepts of letter forms, whereas static stimulation failed to produce perceptible forms.

While the researchers tested only letter-like shapes, they believe that the outlines of other common objects (faces, bodies, houses, and so on) could also be traced using the same principles.

"Advances in technology, including electrical stimulation with high-density grids of electrodes placed on the cortical surface or penetrating into the cortex and non-electrical stimulation with optogenetic, magnetothermal, or focused ultrasound techniques, promise dramatic increases in our ability to stimulate human cortex," the authors note.

"As general-purpose stimulation paradigms, dynamic stimulation and dynamic current steering may be used in combination with any of these technologies to help restore useful visual function to blind people and to permit more efficient transformation of information within other cortical prosthetic applications," they add.

Dr. Bradley Greger of Arizona State University, in Tempe, who studies cortical vision prostheses, told Reuters Health by email, "I think this is some of the most important work being done in the field of neural prosthetics and brain-machine interfaces. Dynamic stimulation makes sense in terms of how electrical stimulation interacts with the tissue of the brain. Demonstrating the effectiveness of the dynamic stimulation in people with profound blindness is a major achievement."

"This team is using a medical device that can be chronically implanted in people with profound blindness to provide visual information directly to the human brain," he said. "This represents the culmination of decades of effort and is a major turning point in the field."

Dr. Greger added, "The same technology also has the potential to restore other senses that have been lost, e.g., touch from spinal cord damage. It also has the potential for use in the treatment of other neurological disorders, e.g., Parkinson's disease and seizure disorders."

Dr. Armin Najarpour Foroushani of the Institute of Biomedical Engineering, Polytechnique Montreal, in Montreal, Canada, who also works with cortical visual prostheses, told Reuters Health by email, "Although still preliminary, this will pave the road for future clinical applications to provide sight for blind individuals. Future efforts can focus on transforming more complex shapes and even videos coming from camera into dynamic and real-time stimulation patterns."

"To test the generalizability of their finding, future works with larger sample size are required in which patients with different levels of visual impairments are participating," he said. "This will also show the reproducibility and reliability of the method."

The study did not have commercial funding. Dr. Yoshor and two colleagues report financial ties to Second Sight Medical Products, a manufacturer of visual cortical prosthetics, and the researchers have filed a patent application related to their work.

Dr. Yoshor did not respond to a request for comments.

SOURCE: Cell, online May 14, 2020.