Human Studies Show Feasibility of Brain-Machine Interfaces

keywords : Neurobiology
date : 3/23/2004
media contact : Dennis Meredith , (919) 681-8054 or (919) 417-6581
dennis.meredith@...

DURHAM, N.C. -- In their first human studies of the feasibility of
using brain signals to operate external devices, researchers at Duke
University Medical Center report that arrays of electrodes can
provide useable signals for controlling such devices. The research
team is now working to develop prototype devices that may enable
paralyzed people to operate "neuroprosthetic" and other external
devices using only their brain signals.

While the new studies provide an initial proof of principle that
human application of brain-machine interfaces is possible, the
researchers emphasize that many years of development and clinical
testing will be required before such neuroprosthetic devices are
available.

The research team, led by neurosurgeon and professor of neurobiology
Dennis Turner, M.D., and neurobiologist Miguel Nicolelis, M.D., will
publish their results in the July 2004 issue of the journal
Neurosurgery. Principal members of the research team also include
Parag Patil, M.D., a resident in neurosurgery and lead author of the
study, and Jose Carmena, Ph.D., a post-doctoral fellow in
neurobiology. The research was supported by the Defense Advanced
Research Projects Agency and the National Institutes of Health.

The research builds on earlier studies in the Nicolelis laboratory,
in which monkeys learned to control a robot arm using only their
brain signals.

In the initial human studies, Patil and colleagues recorded
electrical signals from arrays of 32 microelectrodes, during
surgeries performed to relieve the symptoms of Parkinson's disease
and tremor disorders. These surgical procedures routinely involve
implanting electrodes into the brain and then stimulating the brain
with small electrical currents to relieve the patient's symptoms. The
patients are awake during surgery, and the neurosurgeons typically
record brain signals to ensure that permanent electrodes are placed
into the optimal location in the brain.

In the experiments being reported in Neurosurgery, the researchers
added a simple manual task to the surgical procedure. While brain
signals were recorded using the novel 32-channel electrode array, the
11 volunteer patients were asked to play a hand-controlled video
game.

Subsequently analyzing the signals from these experiments, the team
found that the signals contained enough information to be useful in
predicting the hand motions. Such prediction is the necessary
requisite for reliably using neural signals to control external
devices.

"Despite the limitations on the experiments, we were surprised to
find that our analytical model can predict the patients' motions
quite well," said Nicolelis. "We only had five minutes of data on
each patient, during which it took a minute or two to train them to
the task. This suggests that as clinical testing progresses, and we
use electrode arrays that are implanted for a long period of time, we
could achieve a workable control system for external devices," he
said.

While other researchers have demonstrated that individually implanted
electrodes can be used to control a cursor on a computer screen,
complex external devices would require data from large arrays of
electrodes, said the Duke researchers.

According to Nicolelis, another major difference between the initial
human studies and the monkey studies is that recording in the human
patients were made from electrodes inserted deeper into the brain, in
subcortical structures, rather than the cortical surface.

"This shows that one can extract information not only from cortical
areas, but from subcortical ones, too," said Nicolelis. "This
suggests that in the future, there will be more options for sampling
neuronal information to control a prosthetic device," he said.

According to Turner, the progression to human clinical studies
presents a number of challenges. For example, he said, the data with
monkeys were obtained from electrodes attached to the surface of the
cerebral cortex.

"We initially used subcortical electrodes, because they are more
stable because they are buried deeper," said Turner. Also, he said,
the deeper regions present other advantages. "The way the brain
works, all the signals for motor control are filtered through these
deep regions of the brain before they reach the final cortical
output," he said. "So, they are theoretically easier to record from
than cortical areas. The subcortical areas are also denser, which
means there are more cells to record from in a smaller area.

Working with Duke biomedical engineers, the research team is
currently developing the initial prototype of a neuroprosthetic
device that will include a wireless interface between the patient and
the device.

According to Turner, while the most obvious application of such
technology would be a robot arm for a quadriplegic, he and his
colleagues are planning other devices as well. One would be a
neurally controlled electric wheelchair, and another a neurally
operated keyboard, whose output could include either text or speech.
Such devices could help both paralyzed people and those who have lost
speech capabilities because of stroke or amyotrophic lateral
sclerosis (Lou Gehrig's disease).

A key question in future clinical studies will be whether humans can
incorporate such devices into their "schema," or neural
representation of the external world, said Turner. The monkeys in
Nicolelis' studies appeared to do just that.

"We do know that for all kinds of motor training, such as riding a
bicycle, people incorporate an external device into their schema, and
the process becomes subconscious," he said. "We will build on that
phenomenon in our human studies. It's known, for example, that
patients who don't have use of their arm still show in MRI studies
that the control centers in the brain are working normally. When they
are asked to imagine moving their arm, the control centers become
active. So, we have good hope that the neurons in those centers can
still provide the same signals, even though the arm isn't physically
working."

As their next major step, said Turner, the researchers have already
applied for federal approval to begin implanting experimental
electrode arrays long-term in quadriplegic patients. Such tests,
conducted over the next three to five years would involve implanting
the arrays in specific regions, asking the patients to perform
specific tasks and then exploring which tasks are optimally
controlled by that region.

http://dukemednews.org/news/article.php?id=7493