Macular degeneration (AMD) causes blindness in millions of people in the Western world. It is the most common cause of severe vision loss in the Western world among those aged 50 and over, and its prevalence increases with age. Though there is no cure for AMD, significant recent advancements in artificial retina implants may lead to effective treatment.
Located inside the eye the retina contains light receptors (photoreceptors) which absorb light. Information is then processed and transmitted to the brain. The macula, the central area of the retina, processes most of the information that reaches the brain from the eye, enabling one to see while reading and driving, facial recognition, and any other activity that requires accurate vision. In the peripheral retina, the area of the retina outside the macula that assists mainly with spatial judgment, vision is 10-20 times less precise. In AMD precise vision is impaired due to damage to the center of the retina, while peripheral vision remains normal.
When there is damage to the photoreceptor layers in the retina, an artificial retina -- a device built from tiny electrodes smaller in width than a hair -- may be implanted. Activating these electrodes results in electrical stimulation of the remaining retinal cells and results in visual restoration, albeit partially. AMD patients implanted with an artificial retina possess a combination of artificial central vision and normal peripheral vision. This combination of artificial and natural vision is important to study in order to understand how to help the blind. One of the critical questions in this regard is whether the brain can integrate artificial and natural vision properly.
In a new study published in the journal Current Biology, researchers report for the first time the discovery of evidence indicating that the brain knows how to integrate natural and artificial vision, while maintaining processing information that is important for vision. "We used a unique projection system which stimulated either natural vision, artificial vision or a combination of natural and artificial vision, while simultaneously recording the cortical responses in rodents implanted with a subretinal implant," said the lead author. The implant is composed of dozens of tiny solar cells and electrodes.
Using this model, where prosthetic and natural vision information are combined in the visual cortex, the authors observed striking similarities in the interactions of natural and prosthetic vision, including similar effect of background illumination, linear summation of non-patterned stimuli, and lateral inhibition with spatial patterns, which increased with target contrast. These results support the idea of combined prosthetic and natural vision in restoration of sight for AMD patients.
"These pioneering results have implications for better restoration of sight in AMD patients implanted with retinal prosthetic devices and support our hypothesis that prosthetic and natural vision can be integrated in the brain. The results could also have implications for future brain-machine interface applications where artificial and natural processes co-exist," said the study's senior author.
Brain integrates natural and artificial vision
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