Team deciphers retina's neural code for brain communication to create novel prosthetic retinal device for blind

(Medical Xpress) -- Two researchers at Weill Cornell Medical College have deciphered a mouse's retina's neural code and coupled this information to a novel prosthetic device to restore sight to blind mice. The researchers say they have also cracked the code for a monkey retina — which is essentially identical to that of a human — and hope to quickly design and test a device that blind humans can use.

The breakthrough, reported in the Proceedings of the National Academy of Sciences (PNAS), signals a remarkable advance in longstanding efforts to restore vision. Current prosthetics provide blind users with spots and edges of light to help them navigate. This novel device provides the to restore normal vision. The code is so accurate that it can allow facial features to be discerned and allow animals to track moving images.

The lead researcher, Dr. Sheila Nirenberg, a computational neuroscientist at Weill Cornell, envisions a day when the blind can choose to wear a visor, similar to the one used on the television show Star Trek. The visor's camera will take in light and use a computer chip to turn it into a code that the brain can translate into an image.

"It's an exciting time. We can make blind mouse retinas see, and we're moving as fast as we can to do the same in humans," says Dr. Nirenberg, a professor in the Department of Physiology and Biophysics and in the Institute for Computational Biomedicine at Weill Cornell. The study's co-author is Dr. Chethan Pandarinath, who was a graduate student with Dr. Nirenberg and is currently a postdoctoral researcher at Stanford University.

This new approach provides hope for the 25 million people worldwide who suffer from blindness due to diseases of the retina. Because drug therapies help only a small fraction of this population, prosthetic devices are their best option for future sight."This is the first prosthetic that has the potential to provide normal or near-normal vision because it incorporates the code," Dr. Nirenberg explains.

DISCOVERING THE CODE

Normal vision occurs when light falls on photoreceptors in the surface of the retina. The retinal circuitry then processes the signals from the photoreceptors and converts them into a code of neural impulses. These impulses are then sent up to the brain by the retina's output cells, called . The brain understands this code of neural pulses and can translate it into meaningful images.

Blindness is often caused by diseases of the retina that kill the photoreceptors and destroy the associated circuitry, but typically, in these diseases, the retina's output cells are spared.

Current prosthetics generally work by driving these surviving cells. Electrodes are implanted into a blind patient's eye, and they stimulate the ganglion cells with current. But this only produces rough visual fields.

Many groups are working to improve performance by placing more stimulators into the patient's eye. The hope is that with more stimulators, more ganglion cells in the damaged tissue will be activated, and image quality will improve.

Other research teams are testing use of light-sensitive proteins as an alternate way to stimulate the cells. These proteins are introduced into the retina by gene therapy. Once in the eye, they can target many ganglion cells at once.

But Dr. Nirenberg points out that there's another critical factor. "Not only is it necessary to stimulate large numbers of cells, but they also have to be stimulated with the right code — the code the retina normally uses to communicate with the brain."

This is what the authors discovered — and what they incorporated into a novel prosthetic system.

Dr. Nirenberg reasoned that any pattern of light falling on to the retina had to be converted into a general code — a set of equations — that turns light patterns into patterns of electrical pulses. "People have been trying to find the code that does this for simple stimuli, but we knew it had to be generalizable, so that it could work for anything — faces, landscapes, anything that a person sees," Dr. Nirenberg says.

VISION = CHIP PLUS GENE THERAPY

In a eureka moment, while working on the code for a different reason, Dr. Nirenberg realized that what she was doing could be directly applied to a prosthetic. She and her student, Dr. Pandarinath, immediately went to work on it. They implemented the mathematical equations on a "chip" and combined it with a mini-projector. The chip, which she calls the "encoder" converts images that come into the eye into streams of electrical impulses, and the mini-projector then converts the electrical impulses into light impulses. These light pulses then drive the light-sensitive proteins, which have been put in the ganglion cells, to send the code on up to the brain.

The entire approach was tested on the mouse. The researchers built two prosthetic systems — one with the code and one without.  "Incorporating the code had a dramatic impact," Dr. Nirenberg says. "It jumped the system's performance up to near-normal levels — that is, there was enough information in the system's output to reconstruct images of faces, animals — basically anything we attempted."

In a rigorous series of experiments, the researchers found that the patterns produced by the blind retinas in mice closely matched those produced by normal mouse retinas.

"The reason this system works is two-fold," Dr. Nirenberg says. "The encoder — the set of equations — is able to mimic retinal transformations for a broad range of stimuli, including natural scenes, and thus produce normal patterns of electrical pulses, and the stimulator (the light sensitive protein) is able to send those pulses on up to the brain."

"What these findings show is that the critical ingredients for building a highly-effective retinal prosthetic — the 's code and a high resolution stimulating method — are now, to a large extent, in place," reports Dr. Nirenberg.

Dr. Nirenberg says her retinal prosthetic will need to undergo human clinical trials, especially to test safety of the gene therapy component, which delivers the light–sensitive protein. But she anticipates it will be safe since similar gene therapy vectors have been successfully tested for other retinal diseases.

"This has all been thrilling," Dr. Nirenberg says. "I can't wait to get started on bringing this approach to patients."

The study was funded by grants from the National Institutes of Health and Cornell University's Institute for Computational Biomedicine.

Both Drs. Nirenberg and Pandarinath have a patent application for the prosthetic system filed through Cornell University.

More information: Retinal prosthetic strategy with the capacity to restore normal vision, by Sheila Nirenberg and Chethan Pandarinath, PNAS, dx.doi.org/10.1073/pnas.1207035109

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dan42day
not rated yet Aug 13, 2012
Two blind mice, two blind mice...

This may not only treat blindness but also point the way to the ultimate device/human interface.
andreas_zita
4 / 5 (1) Aug 14, 2012
Does this mean they also can see (and record) what the user sees?
How about dreams? Could those signals be simulated as well?

Sony patented a technique for transmitting visual impressions directly to the brain in 2005. It would be slightly awesome if they could make it real using this new research.
MrVibrating
not rated yet Aug 14, 2012
Gah so what's the "transformation" - Fourier or what!?

Paper's paywalled - anyone got access?

This is extremely exciting but surely the nature of the code deserves a prominent note in the story..?
MrVibrating
not rated yet Aug 14, 2012
MrVibrating
4 / 5 (1) Aug 14, 2012
..so it looks like it may be possible to not only restore vision but also extend its range to encompass other wavelengths, purely on the hardware side. UV / IR modes at the flick of a switch!
MrVibrating
5 / 5 (1) Aug 14, 2012
Two blind mice, two blind mice...

This may not only treat blindness but also point the way to the ultimate device/human interface.
Innit..? Amongst the flurry of new display technologies being developed, this comes along and renders them all obsolete at a stroke... HD, 3D, OLED, Apple's "Retina" (tm) displays (do i smell a lawsuit brewing?), flexible displays... all consigned to the back seat. The future is total immersion via flashing lights and a pill.

Probably.

(um, do i have to have my original retinas ripped out first?)
Tausch
not rated yet Aug 17, 2012
Why stop there?
The code for sterocilia (hairs cells of inner ear) - 'hearing.'
Congrulations to all involved.
MrVibrating
5 / 5 (1) Aug 17, 2012
Great point - and then what about all the other senses? Presumably the precise code will be different for each mode of sensation, but the general principles of 'tuning' the algorithms the researchers have pioneered, you'd think, would be adaptable to any modality.

Other questions remain.. such as neural integration of entirely new prosthetic senses, or, notwithstanding a little nueral plasticity, perhaps even cross-modal reconfiguration - ie. sending video or audio through other distantly related senses (such as sound via somatosensory pathways for example), for those subjects whose traumas are so severe as to preclude direct stimulation (such as complete loss of a sensory organ and/or its main pathway)...
kevinrtrs
1 / 5 (7) Aug 18, 2012
This decentralised decoding and transmission to a central processing centre represents an immense obstacle for evolutionary philosophy. There is currently no known method or mechanism whereby a random process can firstly create an intelligent code and then secondly develop all by natural processes a decoder for that intelligent signal.
There is no way that the two intelligent coding and decoding mechanisms can "evolve" separately - they both have to be present at the same time and with perfect understanding of each other.
To try and imply that it can happen thought some random natural physical/biological process is simply living in fairy land.
I'd like to see how the evolutionists explain the existence of this code and its sender/receiver counterparts.
Tausch
5 / 5 (2) Aug 18, 2012
Thks for the feedback. The areas of reseach to answer kev and Vib's commentary is called adaptic senses or perception - for example: adaptic optics. The procursor to those areas of reseach is brought forth by Vib's coined termed 'new prosethetic senses'.

The only portal to Nature available to us (presently) through our existance and experience is through our existance and experience.
(A 'tiny', limited porttal)

The 'code' is intrinsic to Nature - (to our Models/codes of Nature).
Nothing wrong with this approach until you get questions outside the scope of Models/codes not discovered or created specifically to answer phliosophical tainted questions such as kev's.

Harbor the comforting feeling that 'questions' - inquistiveness - is source and an intrinsic part of our existence and experience - for better or worst - 'till death do us part'. A 'marriage' to Nature.
TheGhostofOtto1923
4.8 / 5 (16) Aug 19, 2012
This decentralised decoding and transmission to a central processing centre represents an immense obstacle for evolutionary philosophy. There is currently no known method or mechanism whereby a random process can firstly create an intelligent code and then secondly develop all by blah
Kevin is just pissed because we don't need Jesus to restore sight to the blind any more. Hey kev they can cure leprosy too, did you know that?