Scientists Restore Movement to Paralyzed
Limbs through Artificial Brain-Muscle Connections
Researchers in a study funded by the National Institutes of Health
(NIH) have demonstrated for the first time that a direct artificial
connection from the brain to muscles can restore voluntary movement
in monkeys whose arms have been temporarily anesthetized. The results
may have promising implications for the quarter of a million Americans
affected by spinal cord injuries and thousands of others with paralyzing
neurological diseases, although clinical applications are years
"This study demonstrates a novel approach to restoring movement
through neuroprosthetic devices, one that would link a person's
brain to the activation of individual muscles in a paralyzed limb
to produce natural control and movements," said Joseph Pancrazio,
Ph.D., a program director at the National Institute of Neurological
Disorders and Stroke (NINDS).
The research was conducted by Eberhard E. Fetz, Ph.D., professor
of physiology and biophysics at the University of Washington in
Seattle and an NINDS Javits awardee; Chet T. Moritz, Ph.D., a post-doctoral
fellow funded by NINDS; and Steve I. Perlmutter, Ph.D., research
associate professor. The results appear in the online Oct. 15 issue
of Nature.[i] The study was performed
at the Washington National Primate Research Center, which is funded
by NIH's National Center for Research Resources.
In the study, the researchers trained monkeys to control the activity
of single nerve cells in the motor cortex, an area of the brain
that controls voluntary movements. Neuronal activity was detected
using a type of brain-computer interface. In this case, electrodes
implanted in the motor cortex were connected via external circuitry
to a computer. The neural activity led to movements of a cursor,
as monkeys played a target practice game.
After each monkey mastered control of the cursor, the researchers
temporarily paralyzed the monkey's wrist muscles using a local
anesthetic to block nerve conduction. Next, the researchers converted
the activity in the monkey's brain to electrical stimulation delivered
to the paralyzed wrist muscles. The monkeys continued to play the
target practice game — only now cursor movements were driven
by actual wrist movements — demonstrating that they had regained
the ability to control the otherwise paralyzed wrist.
The group's approach is one of several lines of current neuroprosthetic
research. Some investigators are using brain-computer interfaces
to record signals from multiple neurons and convert those signals
to control a robotic limb. Other researchers have delivered artificial
stimulation directly to paralyzed arm muscles in order to drive
arm movement — a technique called functional electrical stimulation
(FES). The Fetz study is the first to combine a brain-computer
interface with real-time control of FES.
"A robotic arm would be better for someone whose physical
arm has been lost or if the muscles have atrophied, but if you
have an arm whose muscles can be stimulated, a person can learn
to reactivate them with this technology," says Dr. Fetz.
Until now, brain-computer interfaces were designed to decode the
activity of neurons known to be associated with movement of specific
body parts. Here, the researchers discovered that any motor cortex
cell, regardless of whether it had been previously associated with
wrist movement, was capable of stimulating muscle activity. This
finding greatly expands the potential number of neurons that could
control signals for brain-computer interfaces and also illustrates
the flexibility of the motor cortex.
"The cells don't have to have a preordained role in the movement.
We can create a direct link between the cell and the motor output
that the user can learn to control and optimize over time," says
Dr. Fetz and his colleagues found that the monkeys' control over
neuronal activity — and the resulting control over stimulation
of their wrist muscles — improved significantly with practice.
Practice time was limited by the duration of the nerve block. Comparing
the monkeys' performance during an initial two-minute practice
and a two-minute peak performance period, the scientists found
the monkeys successfully hit the target three times more frequently
and with less error during the peak performance. In the future,
greater control could be gained by using implanted circuits to
create long-lasting artificial connections, allowing more time
for learning and optimizing control, Dr. Fetz says.
The researchers also found that the monkeys could achieve independent
control of both the wrist flexor and extensor muscles.
"An important next step will be to increase the number of
direct connections between cortical cells and muscles to control
coordinated activation of muscles," says Dr. Fetz.
If researchers are able to establish a connection between the
motor cortex and sites in the spinal cord below the injury, people
with spinal injuries may be able to achieve coordinated movements.
Clinical applications are still probably at least a decade away,
according to Dr. Fetz. Better methods for recording cortical neurons
and for controlling multiple muscles must be developed, along with
implantable circuitry that could be used reliably and safely, he
NINDS (www.ninds.nih.gov) is a component of the National Institutes
of Health (NIH), and is the nation's primary supporter of biomedical
research on the brain and nervous system.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.
[i]Moritz, CT, Perlmutter, SI, and Fetz, EE. "Direct Control of
Paralyzed Muscles by Cortical Neurons." Nature, published
online October 15, 2008.