Sheila Nirenberg: A prosthetic eye to treat blindness

100,548 views ・ 2011-12-20

TED


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I study how the brain processes
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information. That is, how it takes
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information in from the outside world, and
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converts it into patterns of electrical activity,
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and then how it uses those patterns
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to allow you to do things --
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to see, hear, to reach for an object.
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So I'm really a basic scientist, not
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a clinician, but in the last year and a half
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I've started to switch over, to use what
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we've been learning about these patterns
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of activity to develop prosthetic devices,
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and what I wanted to do today is show you
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an example of this.
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It's really our first foray into this.
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It's the development of a prosthetic device
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for treating blindness.
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So let me start in on that problem.
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There are 10 million people in the U.S.
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and many more worldwide who are blind
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or are facing blindness due to diseases
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of the retina, diseases like
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macular degeneration, and there's little
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that can be done for them.
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There are some drug treatments, but
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they're only effective on a small fraction
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of the population. And so, for the vast
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majority of patients, their best hope for
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regaining sight is through prosthetic devices.
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The problem is that current prosthetics
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don't work very well. They're still very
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limited in the vision that they can provide.
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And so, you know, for example, with these
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devices, patients can see simple things
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like bright lights and high contrast edges,
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not very much more, so nothing close
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to normal vision has been possible.
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So what I'm going to tell you about today
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is a device that we've been working on
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that I think has the potential to make
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a difference, to be much more effective,
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and what I wanted to do is show you
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how it works. Okay, so let me back up a
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little bit and show you how a normal retina
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works first so you can see the problem
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that we were trying to solve.
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Here you have a retina.
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So you have an image, a retina, and a brain.
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So when you look at something, like this image
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of this baby's face, it goes into your eye
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and it lands on your retina, on the front-end
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cells here, the photoreceptors.
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Then what happens is the retinal circuitry,
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the middle part, goes to work on it,
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and what it does is it performs operations
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on it, it extracts information from it, and it
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converts that information into a code.
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And the code is in the form of these patterns
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of electrical pulses that get sent
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up to the brain, and so the key thing is
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that the image ultimately gets converted
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into a code. And when I say code,
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I do literally mean code.
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Like this pattern of pulses here actually means "baby's face,"
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and so when the brain gets this pattern
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of pulses, it knows that what was out there
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was a baby's face, and if it
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got a different pattern it would know
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that what was out there was, say, a dog,
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or another pattern would be a house.
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Anyway, you get the idea.
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And, of course, in real life, it's all dynamic,
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meaning that it's changing all the time,
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so the patterns of pulses are changing
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all the time because the world you're
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looking at is changing all the time too.
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So, you know, it's sort of a complicated
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thing. You have these patterns of pulses
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coming out of your eye every millisecond
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telling your brain what it is that you're seeing.
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So what happens when a person
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gets a retinal degenerative disease like
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macular degeneration? What happens is
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is that, the front-end cells die,
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the photoreceptors die, and over time,
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all the cells and the circuits that are
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connected to them, they die too.
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Until the only things that you have left
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are these cells here, the output cells,
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the ones that send the signals to the brain,
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but because of all that degeneration
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they aren't sending any signals anymore.
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They aren't getting any input, so
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the person's brain no longer gets
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any visual information --
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that is, he or she is blind.
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So, a solution to the problem, then,
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would be to build a device that could mimic
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the actions of that front-end circuitry
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and send signals to the retina's output cells,
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and they can go back to doing their
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normal job of sending signals to the brain.
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So this is what we've been working on,
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and this is what our prosthetic does.
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So it consists of two parts, what we call
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an encoder and a transducer.
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And so the encoder does just
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what I was saying: it mimics the actions
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of the front-end circuitry -- so it takes images
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in and converts them into the retina's code.
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And then the transducer then makes the
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output cells send the code on up
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to the brain, and the result is
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a retinal prosthetic that can produce
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normal retinal output.
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So a completely blind retina,
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even one with no front-end circuitry at all,
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no photoreceptors,
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can now send out normal signals,
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signals that the brain can understand.
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So no other device has been able
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to do this.
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Okay, so I just want to take
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a sentence or two to say something about
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the encoder and what it's doing, because
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it's really the key part and it's
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sort of interesting and kind of cool.
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I'm not sure "cool" is really the right word, but
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you know what I mean.
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So what it's doing is, it's replacing
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the retinal circuitry, really the guts of
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the retinal circuitry, with a set of equations,
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a set of equations that we can implement
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on a chip. So it's just math.
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In other words, we're not literally replacing
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the components of the retina.
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It's not like we're making a little mini-device
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for each of the different cell types.
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We've just abstracted what the
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retina's doing with a set of equations.
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And so, in a way, the equations are serving
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as sort of a codebook. An image comes in,
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goes through the set of equations,
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and out comes streams of electrical pulses,
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just like a normal retina would produce.
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Now let me put my money
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where my mouth is and show you that
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we can actually produce normal output,
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and what the implications of this are.
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Here are three sets of
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firing patterns. The top one is from
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a normal animal, the middle one is from
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a blind animal that's been treated with
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this encoder-transducer device, and the
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bottom one is from a blind animal treated
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with a standard prosthetic.
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So the bottom one is the state-of-the-art
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device that's out there right now, which is
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basically made up of light detectors,
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but no encoder. So what we did was we
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presented movies of everyday things --
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people, babies, park benches,
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you know, regular things happening -- and
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we recorded the responses from the retinas
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of these three groups of animals.
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Now just to orient you, each box is showing
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the firing patterns of several cells,
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and just as in the previous slides,
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each row is a different cell,
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and I just made the pulses a little bit smaller
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and thinner so I could show you
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a long stretch of data.
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So as you can see, the firing patterns
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from the blind animal treated with
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the encoder-transducer really do very
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closely match the normal firing patterns --
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and it's not perfect, but it's pretty good --
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and the blind animal treated with
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the standard prosthetic,
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the responses really don't.
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And so with the standard method,
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the cells do fire, they just don't fire
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in the normal firing patterns because
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they don't have the right code.
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How important is this?
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What's the potential impact
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on a patient's ability to see?
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So I'm just going to show you one
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bottom-line experiment that answers this,
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and of course I've got a lot of other data,
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so if you're interested I'm happy
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to show more. So the experiment
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is called a reconstruction experiment.
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So what we did is we took a moment
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in time from these recordings and asked,
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what was the retina seeing at that moment?
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Can we reconstruct what the retina
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was seeing from the responses
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from the firing patterns?
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So, when we did this for responses
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from the standard method and from
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our encoder and transducer.
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So let me show you, and I'm going to
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start with the standard method first.
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So you can see that it's pretty limited,
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and because the firing patterns aren't
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in the right code, they're very limited in
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what they can tell you about
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what's out there. So you can see that
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there's something there, but it's not so clear
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what that something is, and this just sort of
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circles back to what I was saying in the
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beginning, that with the standard method,
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patients can see high-contrast edges, they
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can see light, but it doesn't easily go
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further than that. So what was
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the image? It was a baby's face.
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So what about with our approach,
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adding the code? And you can see
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that it's much better. Not only can you
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tell that it's a baby's face, but you can
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tell that it's this baby's face, which is a
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really challenging task.
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So on the left is the encoder
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alone, and on the right is from an actual
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blind retina, so the encoder and the transducer.
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But the key one really is the encoder alone,
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because we can team up the encoder with
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the different transducer.
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This is just actually the first one that we tried.
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I just wanted to say something about the standard method.
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When this first came out, it was just a really
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exciting thing, the idea that you
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even make a blind retina respond at all.
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But there was this limiting factor,
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the issue of the code, and how to make
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the cells respond better,
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produce normal responses,
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and so this was our contribution.
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Now I just want to wrap up,
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and as I was mentioning earlier
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of course I have a lot of other data
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if you're interested, but I just wanted to give
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this sort of basic idea
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of being able to communicate
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with the brain in its language, and
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the potential power of being able to do that.
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So it's different from the motor prosthetics
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where you're communicating from the brain
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to a device. Here we have to communicate
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from the outside world
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into the brain and be understood,
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and be understood by the brain.
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And then the last thing I wanted
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to say, really, is to emphasize
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that the idea generalizes.
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So the same strategy that we used
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to find the code for the retina we can also
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use to find the code for other areas,
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for example, the auditory system and
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the motor system, so for treating deafness
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and for motor disorders.
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So just the same way that we were able to
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jump over the damaged
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circuitry in the retina to get to the retina's
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output cells, we can jump over the
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damaged circuitry in the cochlea
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to get the auditory nerve,
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or jump over damaged areas in the cortex,
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in the motor cortex, to bridge the gap
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produced by a stroke.
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I just want to end with a simple
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message that understanding the code
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is really, really important, and if we
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can understand the code,
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the language of the brain, things become
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possible that didn't seem obviously
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possible before. Thank you.
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09:54
(Applause)
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