The new study builds upon recent discoveries with high-resolution implants. By placing these into the visual cortex of the human brain enables the brain to recognize artificially induced shapes and percepts (the objects of perception).
The visual cortex of the brain refers to that area of the cerebral cortex which can process visual information. This region is located in the occipital lobe, connected to the visual nerves that run directly from the eye to the primary visual cortex to the Visual Association cortex.
Old concept new application
The concept of stimulating the brain through the use of an implant to generate artificial visual objects was developed during the 1970s. These early systems were limited in terms of the size and detail of the images, hampered by the limitation of only being able to generate a tiny number of pixels at any point in time.
These earlier concepts have been expanded upon and developed by scientists based at the Netherlands Institute for Neuroscience. This was made possible through strides made with microchip fabrication and microelectronics. Not only are these newer devices able to provide improved resolution, they have been shown to be more stable and durable.
The science behind it
In terms of the underpinning technology as an electrical stimulation is directed into the brain through an implanted electrode, this process generates the percept of a dot of light, appearing at a particular location wit in visual space. This is known as a 'phosphene.'
Phosphene refers to a sensation of a ring or spot of light that is produced through the application of pressure onto the eyeball or, as in the case of the research under discussion, from the direct stimulation of the visual system other than by light.
Based on this principle, the scientists fabricated the high-resolution implants formed of 1024 electrodes. The electrodes were implanted into the the visual cortex of two test subject sighted monkeys. The aim here was to create interpretable images through the delivery of electrical stimulation simultaneously through multiple electrodes.
This process led to the generation of a percept that was composed of multiple phosphenes. It was found that varying the number of electrodes implanted into the visual cortex varied the number of artificial pixels that can be generated.
The chip is an example of neuroprosthetics. These are brain-computer interfaces that can be used to assist those with motor or sensory disabilities to regain a degree of control of their senses. This is through making a connection between the brain and a computer. This is achieved through brain training, and, in essence the power of thought.
In order to assess the effectiveness of the implants, the researchers required the monkeys to undergo several tests. This included having the monkeys perform a behavioral task where they were required to make eye movements in order to report the location of a phosphene. The phosphene was elicited through electrical stimulation which was triggered by an individual electrode.
Following this, the monkeys were challenged on more complex tasks, including a direction-of-motion task. For this, micro-stimulation was triggered via a sequence of electrodes. Another task undertaken by the monkeys was a letter discrimination task. For this, micro-stimulation was delivered across 8-15 electrodes at the same time. The effect of this was to create a percept in the form of a letter. The monkeys were able to recognize shapes and percepts, such as lines, moving dots, and letters, using their artificial vision.
Based on the research to date the hope remains that the restoration of vision in blind people through a brain implant could be on the verge of becoming reality. The essential feature of the technology is showing that it is possible to visualize images through by-passing both the eye and the optic nerve.
The research has been published in the journal Science
. The peer reviewed paper is titled “Shape perception via a high-channel-count neuroprosthesis in monkey visual cortex.”
This article forms part of Digital Journal’s long-running Essential Science series, where new research relating to wider science stories of interest are presented on a weekly basis.
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