Sensitive Implants Help You Adjust
Your Grip
Source: New Scientist
NERVE implants can help paralysed people perform simple
tasks, such as gripping a cup. But the lack of feedback means they can
drop the cup or even crush it. Now Danish scientists say they have
found a way to help people grip more effectively. They hope eventually
to help restore sensation to
those with spinal injuries.
Without sensation, patients using neural prostheses have
to rely upon their eyes and experience: grip an object too forcefully
and they risk muscle fatigue, too gently and they drop it. This is one
of the biggest problems with bionic implants, says Morten Haugland at
the Center for Sensory-Motor Interaction at Aalborg University.
Haugland and his colleague Andreas Inmann have developed
a portable system that monitors bundles of nerves from the index
finger of a patient to detect overexertion and compensate by adjusting
their grip. The system has been designed to work with commercial
neural prostheses such as the Freehand
muscle stimulator, which helps quadriplegics. Such systems work by
electrically stimulating particular muscles, causing them to contract
and making it possible to achieve coordinated movements. This, says
Haugland, can help patients carry out everyday tasks that would
otherwise be impossible, such as eating with a fork.
But while such devices can help to improve a patient's
quality of life, Haugland says they can be frustrating as well. Anyone
who has tried drinking after a mouth-numbing visit to the dentist
knows how hard it is to use muscles when there is no sensation to tell
you what they are doing.
Haugland's add-on device consists of three electrodes
wrapped around a nerve bundle implanted into the palm of the hand.
Information on the strength of grip is fed back to the muscle
stimulator, located externally on a wrist cuff.
The stimulator is controlled by two buttons pressed by a
head-mounted prodder: one turns the system on and increases the power,
the other decreases the power and turns it off. There are systems that
do this using artificial sensors embedded in gloves, but it makes far
more sense to use the sensors in your own fingers, says Haugland.
Patients tend to crank the system up to full power all
the time, says Haugland. But this isn't necessary: prodding a potato
with a fork may require a strong grip, but carrying it to your mouth
does not. "Our system makes sure you use the right amount of force,"
he says.
His team's ultimate goal is to restore a patient's
sensation, but for now they are planning to exploit the new approach.
Haugland is using similar electrodes to help paraplegics balance when
standing.
Haugland's system uses the hand as an extension to a
machine--with muscles instead of motors, and nerves replacing touch
sensors. But this is effectively what is going on normally when we
grasp objects, says Gerald Loeb, a biomedical engineer and expert in
neural prosthetics at the University of Southern California in Los
Angeles. "When you grasp an object you do not think about the details
of what muscles to contract," he says.
http://www.newscientist.com/news/news.jsp?id=ns224225