A
new Northwestern Medicine brain-machine technology delivers messages
from the brain directly to the muscles—bypassing the spinal cord—to
enable voluntary and complex movement of a paralyzed hand. The device
could eventually be tested on, and perhaps aid, paralyzed patients.
“We
are eavesdropping on the natural electrical signals from the brain that
tell the arm and hand how to move, and sending those signals directly
to the muscles,” said Lee E. Miller, the Edgar C. Stuntz Distinguished
Professor in Neuroscience at Northwestern University Feinberg School of
Medicine and the lead investigator of the study, which was published in Nature.
“This connection from brain to muscles might someday be used to help
patients paralyzed due to spinal cord injury perform activities of daily
living and achieve greater independence.”
The
research was done in monkeys, whose electrical brain and muscle signals
were recorded by implanted electrodes when they grasped a ball, lifted
it and released it into a small tube. Those recordings allowed the
researchers to develop an algorithm or “decoder” that enabled them to
process the brain signals and predict the patterns of muscle activity
when the monkeys wanted to move the ball.
These
experiments were performed by Christian Ethier, a post-doctoral fellow,
and Emily Oby, a graduate student in neuroscience, both at the Feinberg
School of Medicine. The researchers gave the monkeys a local anesthetic
to block nerve activity at the elbow, causing temporary, painless
paralysis of the hand. With the help of the special devices in the brain
and the arm—together called a neuroprosthesis—the monkeys’ brain
signals were used to control tiny electric currents delivered in less
than 40 milliseconds to their muscles, causing them to contract, and
allowing the monkeys to pick up the ball and complete the task nearly as
well as they did before.
“The
monkey won’t use his hand perfectly, but there is a process of motor
learning that we think is very similar to the process you go through
when you learn to use a new computer mouse or a different tennis
racquet. Things are different and you learn to adjust to them,” said
Miller, also a professor of physiology and of physical medicine and
rehabilitation at Feinberg and a Sensory Motor Performance Program lab
chief at the Rehabilitation Institute of Chicago.
Because
the researchers computed the relationship between brain activity and
muscle activity, the neuroprosthesis actually senses and interprets a
variety of movements a monkey may want to make, theoretically enabling
it to make a range of voluntary hand movements.
“This gives the monkey voluntary control of his hand that is not possible with the current clinical prostheses,” Miller said.
The
Freehand prosthesis is one of several prostheses available to patients
paralyzed by spinal cord injuries that are intended to restore the
ability to grasp. Provided these patients can still move their
shoulders, an upward shrug stimulates the electrodes to make the hand
close, a shrug down stimulates the muscles to make the hand open. The
patient also is able to select whether the prosthesis provides a power
grasp in which all the fingers are curled around an object like a
drinking glass, or a key grasp in which a thin object like a key is
grasped between the thumb and curled index finger.
In
the new system Miller and his team have designed, a tiny implant called
a multi-electrode array detects the activity of about 100 neurons in
the brain and serves as the interface between the brain and a computer
that deciphers the signals that generate hand movements.
“We
can extract a remarkable amount of information from only 100 neurons,
even though there are literally a million neurons involved in making
that movement,” Miller said. “One reason is that these are output
neurons that normally send signals to the muscles. Behind these neurons
are many others that are making the calculations the brain needs in
order to control movement. We are looking at the end result from all
those calculations.”
The
research was supported by the National Institutes of Health/NINDS grant
#NS053603, the Chicago Community Trust through the Searle Program for
Neurological Restoration at the Rehabilitation Institute of Chicago, and
the Fonds de rechereche en santé du Quebec.
Source: Northwestern University
