Monkeys adapt robot arm as their own

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Monkeys adapt robot arm as their own

11 May 2005 Medical News Today

Monkeys that learn to use their brain signals to control a robotic

arm are not just learning to manipulate an external device, Duke

University Medical Center neurobiologists have found. Rather, their

brain structures are adapting to treat the arm as if it were their

own appendage.

The finding has profound implications both for understanding the

extraordinary adaptability of the primate brain and for the potential

clinical success of brain-operated devices to give the handicapped

the ability to control their environment, said the researchers.

Led by neurobiologist lis of Duke's Center for

Neuroengineering, the researchers published their findings in the May

11, 2005, issue of the Journal of Neuroscience. Lead author on the

paper was Mikhail Lebedev in lis's laboratory. Other coauthors

were Carmena, ph O'Doherty, Miriam Zacksenhouse, Craig

Henriquez and Principe. The work was supported by the Defense

Advanced Research Projects Agency, the S. McDonnel Foundation,

the National Institutes of Health, the National Science Foundation

and the Reeve Paralysis Foundation.

In the study, Lebedev performed detailed analysis of the mass of

neural data that emerged from experiments reported in 2003, in which

the researchers discovered for the first time that monkeys were able

to control a robot arm with only their brain signals.

In those experiments, the researchers first implanted an array of

microelectrodes -- each thinner than a human hair -- into the frontal

and parietal lobes of the brains of two female rhesus macaque

monkeys. The faint signals from the electrode arrays were detected

and analyzed by the computer system the researchers developed to

recognize patterns of signals that represented particular movements

by an animal's arm.

In the initial behavioral experiments, the researchers recorded and

analyzed the output signals from the monkeys' brains as the animals

were taught to use a joystick to both position a cursor over a target

on a video screen and to grasp the joystick with a specified force.

After the animals' initial training, however, the researchers made

the cursor more than a simple display. They incorporated into its

movement the dynamics, such as inertia and momentum, of a robot arm

functioning in another room. While the animals' performance initially

declined when the robot arm was included in the feedback loop, they

quickly learned to allow for these dynamics and became proficient in

manipulating the robot-reflecting cursor, found the scientists.

The scientists next removed the joystick, after which the monkeys

continued to move their arms in mid-air to manipulate and " grab " the

cursor, thus controlling the robot arm. However, after a few days,

the monkeys realized that they did not need to move their own arms.

Their arm muscles went completely quiet, they kept the arm at their

side, and they controlled the robot using only their brain and visual

feedback.

" After these experiments, a major question remained about how the

animals' brains adapted to the transition between joystick and brain

control, " said lis. " Thus, drawing on the extensive data from

these experiments Mikhail analyzed very carefully what happens

functionally to the brain cells and the brain cell ensembles in

multiple brain areas during this transition.

" And basically we were able to show clearly that a large percentage

of the neurons become more 'entrained' -- that is, their firing

becomes more correlated to the operation of the robot arm than to the

animal's own arm. "

According to lis, the analysis revealed that, while the animals

were still able to use their own arms, some brain cells formerly used

for that control shifted to control of the robotic arm.

" Mikhail's analysis of the brain signals associated with use of the

robotic and animals' actual arms revealed that the animal was

simultaneously doing one thing with its own arm and something else

with the robotic arm, " he said. " So, our hypothesis is that the

adaptation of brain structures allows the expansion of capability to

use an artificial appendage with no loss of function, because the

animal can flip back and forth between using the two. Depending on

the goal, the animal could use its own arm or the robotic arm, and in

some cases both.

" This finding supports our theory that the brain has extraordinary

abilities to adapt to incorporate artificial tools, whether directly

controlled by the brain or through the appendages " said

lis. " Our brain representations of the body are adaptable

enough to incorporate any tools that we create to interact with the

environment. This may include a robot appendage, but it may also

include using a computer keyboard or a tennis racket. In any such

case, the properties of this tool become incorporated into our

neuronal 'space', " he said. According to lis, such a theory of

brain adaptability has been controversial.

" Few researchers have been willing to go as far as postulating such

extraordinary adaptability for the brain and how important this

adaptability of brain circuitry is in enabling us to learn to use

tools, " he said. " It has long been appreciated that adaptability is a

key capability of the prefrontal cortex that is a hallmark of the

human brain. It gives us the ability to design, create, and use tools

to do everything from lift massive weights to make microscopic

manipulations.

" What Mikhail, I and our colleagues are suggesting is that a

fundamental trait of higher primates, in particular apes and humans,

is the ability to incorporate these tools into the very structure of

the brain. In fact, we're saying that it's not only the brain that is

adaptable; it's the whole concept of self. And this concept of self

extends to our tools. Everything from cars to clothing that we use in

our lives becomes incorporated into our sense of self. So, our

species is capable of 'evolving' the perception of what we are.

" From a philosophical point of view, we're saying that the sense of

self is not limited to our capability for introspection, our sense of

our body limits, and to the experiences we've accumulated, " lis

said. " It really incorporates every external device that we use to

deal with the environment. " The findings also have important clinical

significance, said lis.

" The experiments we have conducted not only represent a proof of

concept that such an external device can be directly controlled in a

clinical setting, " he said. " This latest analysis shows that the

device is incorporated very intimately as a natural extension of the

brain. This is a fundamentally important property if brain-machine

interface technology is to have any clinical future. If the brain was

essentially static, then paralyzed people would never be able to

adapt to operate external devices with enough dexterity to make them

really useful. "

Importantly, said lis, truly useful " neuroprosthetic " devices

will have to be dexterous enough to give patients a full range of

mobility in robot arms, hands or other appendages. " Our studies show

that it will not be enough to implant a few electrodes, measure a few

signals and attain sufficient capability for useful devices, " he

said. " The ability to merely move a cursor on a screen or open or

close an artificial hand is not enough to justify the use of such

systems. " Rather, he said, the objective in his laboratory is to

develop devices that offer paralyzed people fully functional

artificial appendages.

For example, he said, new experiments in his laboratory seek to

enable the brain to perceive a feedback sensation from

neuroprosthetic devices. Such feedback might be in the form of visual

information on the effects of moving a robotic arm. Or, it might be

tactile feedback fed as signals into electrodes implanted in the

brain.

Such feedback would greatly enhance people's ability to learn and use

the devices, said lis. Also, such feedback would expand use of

neuroprosthetics to amputees, because the devices would include all

the features -- including feedback -- of real appendages.

" In our new experiments, the idea is that by using vision and touch,

we're actually going to create inside the brains of these animal a

vivid perceptual image of what it is to have a third arm, " he said.

Duke University Medical Center

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