NeuroProsthetics

NeuroProsthetics

Steven L. Fries, CPO

Meet the mind readers

Paralysed people can now control artificial limbs by thought alone. Ian
Sample reports

Thursday March 31, 2005
The Guardian

There's a hand lying on the blanket on Matt Nagle's desk and he's staring at
it intently, thinking Close, close, as the scientists gathered around him
look on. To their delight, the hand twitches and its outstretched fingers close
around the open palm, clenching to a fist.
In that moment, Nagle made history. Paralysed from the neck down after a
vicious knife attack four years ago, he is the first person to have controlled an
artificial limb using a device chronically implanted into his brain.
The experiment took place a few months ago as part of a broader trial into
what are known in the business as brain-computer interfaces. Although it is
early days, aficionados of the technology see a world where brain implants return
ability to those with disability, allowing them to control all manner of
devices by thought alone. There are huge hurdles ahead. No one knows how much
information we can usefully decipher from the electrical fizz of the brain's 100bn
neurons. More importantly, scientists are still in the dark as to what effect,
if any, long term implants will have on the human brain, or how its circuitry
will cope with the new tasks demanded of it.
Nagle got involved in the latest trial after hearing about John Donoghue, a
professor of neuroscience at Brown University on Rhode Island, whose company
Cyberkinetics has developed an implant called BrainGate. Under Donoghue's
instruction, Nagle was given a general anaesthetic before a disc the size of a poker
chip was cut from his skull. After making an incision in the brain's
protective membrane, a tiny array of 96 hair-thin electrodes, each protruding about a
millimetre, was pressed onto the surface of his brain, just above a region of
the sensory motor cortex that is home to the neuronal circuitry governing arm
and hand movement. With the electrodes in position, the bony disc was
replaced, leaving room for a tiny wire to connect the electrodes to a metal plate the
size of a 10p piece that sits on Nagle's head like a button.
To read brain signals from Nagle's motor cortex, Donoghue's researchers
attach an amplifier to the metallic button on his head and run a cable to a
computer. When he's hooked up, the tiny voltages of the sparking neurons beneath the
electrodes produce a series of brainwaves that dance on the computer screen.
Since having the electrodes implanted in June last year, Nagle has been
test-driving the technology, seeing what he, and it, are capable of. We're
evaluating his ability to do a whole range of things. We've hooked him to a computer
that lets him turn a TV on and off, change channel and turn the volume up and
down, says Donoghue.
The success of the technology relies on being able to decipher accurately the
electrical activity within Nagle's brain and turn it into useful actions. The
trials started tentatively. Nagle had been unable to move any of his limbs
for nearly four years. The scientists had no idea how this would have affected
the brain signals that normally control movement. Would they have fizzled out
through lack of use, much as muscles waste away in the wheelchair-bound? No
one knew if it would work in someone with these injuries, but simply by asking
him to imagine moving we got useful signals and it was amazing. I was
overwhelmed by how beautifully the cells were still working, says Donoghue.
Getting the signals is one thing; deciphering them is another. But Donoghue's
team found that some simple rules held - if the brain wanted to move the hand
to the right, certain cells would fire a rapid series of impulses. If the
brain was willing the hand to move left, the cells fired a different number of
times. Other information, such as where the hand should end up, what trajectory
it should take, and how quickly it should move, is also embedded in the
electrical signals.
Part of the difficulty in reading brain signals is that while even a simple
movement such as raising a hand requires electrical signals from many regions
of the brain, the implanted electrodes pick up just a tiny fraction of those
that fire. We're recording only a dozen or so, when a million might be active,
says Donoghue, who likens the process to dropping a microphone into a crowded
room and trying to get the gist of all the conversations going on.
The limitations of taking signals from just a few active neurons have become
apparent in the trial. Many of the tasks Nagle is set involve moving a cursor
around a screen by thinking which way it should move. But the cursor jiggles,
making it difficult to select icons on the screen with any precision. We
could smooth it out using software, but at the moment, we want to see if Matthew
can learn to control the wobble, says Donoghue, who is recruiting four other
patients to complete the trial. If he can do that, he can use computer
software to answer emails, and if he can do that, he could be employed.
Ultimately, Donoghue says there should be no need to connect cables to
peoples' heads to read their minds. Miniaturisation should bring smaller devices
that can be powered through unbroken skin and transmit signals wirelessly from
the brain to a processor worn on a belt that triggers the intended device.
If all goes according to plan, Donoghue's trial, designed to explore how well
a variety of people can control different devices by the power of thought,
will be completed in about 18 months. He's not the only one keen to find out
just how useful such devices could be. At Duke University in North Carolina,
Miguel Nicolelis is in the final stages of getting permission to fit 16
quadriplegic patients - half in the US, half in Brazil - with brain implants for a
period of 30 days. Initially the trial will look at whether the patients' brains
still produce useful motor signals. Then, we want to see if these patients can
control a robotic arm that can reach and grab objects, and how well their
brains get used to it, says Nicolelis.
In previous studies, his team showed that when monkeys had their brains
hooked up to robotic arms, they assimilated the arm, effectively making it their
own. Their brains actually incorporated the robotic arm by dedicating neuronal
space to it. We want to see if the same thing happens in humans, he adds.
For all the promise brain implants hold, there are some that believe they are
not the best bet for many patients. Implants suffer from a number of
drawbacks, the first being that they demand invasive surgery, with attendant risks.
Second, implanted electrodes cause at least some inflammation of the brain
tissues they push into. As well as obvious medical concerns, if the inflammation is
significant, it can smother any signals the electrodes might pick up.
Every one you put in gives some inflammation, but it's minor. We're still
working on making electrodes more biocompatible, but we've got monkeys who have
so far survived for nearly five years with implants and they are fine, says
Nicolelis. The thing is, to do what we want to do, to get that level of
control, you have to get into the brain.
Nicolelis says his goal is to use brain implants to allow the disabled to
walk again. He has already started designing a wearable robotic exoskeleton
that could help power paralysed legs - think Wallace and Gromit's The Wrong
Trousers, only with better control. Nicolelis is also developing something called
shared control in which a robotic limb is triggered by a basic command from
the brain, but refines and carries out the movement itself, using
pre-programmed intelligence. The hurdles ahead, after finding even better electrodes, are
developing prosthetics that are more amenable to brain control, he says.
Many of the labs looking at brain implants started out doing basic research
into understanding how small numbers of neurons worked. The research required
the development of thin wire electrodes that could cosy up to individual
neurons, a legacy that led to fully implantable devices. But for many applications,
simpler signals, that can be picked up without undergoing major surgery, may
suffice.
At the Wadsworth Centre, the laboratory arm of the New York State health
department, John Wolpaw and his team recently proved that a hat not unlike a
swimming cap peppered with electrodes could pick up clear enough signals to allow
the wearer to move a cursor around a computer screen. There was an unsupported
assumption that to get that kind of control, you needed to implant, but our
work showed that's not the case. These systems can do better than a lot of
people give them credit for, says Wolpaw.
Instead of tapping into the brain's natural signals for moving limbs,
Wolpaw's system picks up changes in general brain activity that the patient must
learn to control. We look at rhythms on the EEG that are normally just idling,
but we've shown that by using mental imagery, people can learn to make the
signals stronger or weaker and we can translate that into cursor movement, says
Wolpaw.
Wolpaw's patients are trained over 10 sessions, during which about 80% learn
to control their brainwaves well enough to move a cursor around a screen. In
time, most can do other things, such as think of answers to questions to select
on screen, without it interrupting their control. The risks of the technique
are undoubtedly fewer than for full brain implants, though questions remain
about the effects of forcing the brain to change its activity, in a way the
electrodes can pick up. It's probably just like learning anything else. There's
been no indication that any of this does anything harmful, and it's hard to see
how it could, but we can't say for sure, says Wolpaw.
While Wolpaw has achieved control many thought impossible without implanting
electrodes directly into the brain, he feels a third technique, called
electrocorticography, or Ecog, might have the brightest future. Ecog involves a
smaller operation to place a small sheet of electrodes on the surface of the brain.
With this, you get strong signals, you can pick them up from smaller areas
but you're not sticking something into the brain, he says. Preliminary trials
show patients can learn to use Ecog devices much faster than electrodes placed
on their scalps.
More than likely is that all three techniques will co-develop, each finding
its own niche. Full implants may only be worthwhile for the severely disabled,
who need to control complex machinery, such as prosthetic limbs, with their
thoughts. For many though, regaining even the most minor level of independence
would help. One fellow said to me, 'I just want to be able to scratch my
nose', says Donoghue. It's easy to forget the kinds of extraordinary things
people can't accomplish. If you can do something that lets them reach out to the
world even a little, it can make a huge difference.

· What did you think of this article? Mail your responses to
<Email Address Redacted> and include your name and address.