Reacción a "Electrodes capable of evoking vision and adapting in real time are implanted in the brains of two blind people"

The paper represents a significant step forward in visual prosthesis technology. The quality of the research appears high, demonstrated by the careful, rigorous experimental design and detailed reporting, especially given the challenges inherent in working with human subjects. It is a technically sophisticated piece of work and marks a meaningful advancement that can be applied to other approaches as well.

Context: Cortical visual prostheses aim to restore some visual perception in individuals with blindness caused by diseases of the eyes.  As the field advances toward higher and higher resolution devices, two critical questions have been raised by researchers.  The first is, how can we know, objectively, what the perceptual result is from applying a given level of stimulation to a given electrode so we can calibrate how much is needed?  The second is, how can we make that assessment for the thousands of electrodes needed for high resolution artificial vision, without placing an unreasonable burden on the patient?

New Information: This paper directly addresses both of those two questions for cortical implants that are in the form of a grid of electrodes, like the Utah array the authors used.  They were able to show that if they stimulate from one electrode, or a small cluster of neighboring electrodes, while simultaneously recording from surrounding electrodes, the neural activity from the recordings can be matched to the reports from the patient of what they see. Thus, they conclude that the amount of electrical current required to create a visual percept, a phosphene, which varies from electrode to electrode, and even individual to individual, can be automatically deduced in a rapid manner.  

The authors have shown that recordings from neurons near a stimulation electrode reliably reflect the characteristics of generated phosphenes.

Implications: By providing a means for objectively assessing generated perceptions, the authors appear to have solved two important outstanding problems in the field of artificial vision: how to reliably calibrate stimulation current for a given electrode, including recalibrations that might be needed in long-term implants, and how to automate that calibration in a way that appears to be useful for implants with many, many electrodes.

Incremental Advance: The fact that these results are obtained in human patients makes this a substantially more impactful finding than preclinical studies alone. 

Important limitations to consider:

• The Utah arrays used in this work are 10 x 10 grids of electrodes. If each electrode generates a single phosphene, the pixels of artificial vision, that is (a) not very high resolution, and (b) would cover only a small part of the visual scene.  Using a single array like this would be like having blurry vision, looking through a small tube. Multiple arrays can be combined to enhance the coverage of the visual field, but the current technology behind that would mean there would be only small, isolated islands of vision, rather than a continuous visual field.
• Early stage with limited patient sample: While this represents a substantial advance, it is still an early stage. The results are based on data from only two patients, which limits the generalizability of the findings. The results are strong enough that we would expect to see other teams adopt the proposed strategies and confirm these results.
• Patient variability: While the results from the two subjects were largely consistent, there was some variability.  That variability needs to be explored in a larger patient population to understand how well these ideas will generalize.  The visual cortex and its response to stimulation varies significantly between individuals.  These findings might need adjustment to be universally applicable.
• Electrode lifetime: A key challenge for visual prostheses is ensuring the long-term biocompatibility of the electrodes. Chronic inflammation and tissue scarring can degrade performance over time. The paper does not address this issue directly and it is a crucial factor for future development.  While the Utah array has been shown to be biocompatible, there are recent concerns about loss of effectiveness over the span of years.  The experiments here were conducted with implants that were in place for only 6 months, so do not address that problem.
• Perceptual interpretation: Even with precise stimulation, the patient's brain must still interpret the patterns. This process can be influenced by prior visual experience and cognitive factors.  While visual prostheses, especialy cortical ones, have shown some promise to create useful artificial vision, there is much to be learned about how the brain interprets that new input. This study examined the creation of individual phosphenes, rather than shapes or visual scenes.
• Surgical risks and complexity: Implantation of cortical prostheses is a complex and invasive surgical procedure. Associated risks and long-term complications need to be carefully considered. This work reduces the potential risks somewhat by proposing a way to solve the problems listed above without additional implants.

This research represents an impressive advancement in cortical visual prosthesis technology, creating a means for automatically measuring the capacity of individual electrodes in an array to generate phosphenes, the pixels of artificial vision.

These results have solved one of the large outstanding problems in designing high-resolution artificial vision, eliminating one of the major barriers to designing visual prostheses that will have wide-spread acceptance by potential recipents.