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 Hooking Neuroprosthetics to the limbs

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Date posted: 27/12/2006

Neuroprosthetic devices have had some concrete success stories in recent years, and the stage is finally set for developing them, not to just monitor and interact with brain signals, but control external body parts as well. The Functional Electrical Stimulation Centre, at Louis Stokes Veterans Affairs Medical Centre, in Cleveland, Ohio, is working on the construction of a device that records brain signals and transmits them to paralysed muscles, potentially returning muscle control to severely paralysed patients.

The system is split into several separate parts, which must communicate efficiently. An embedded brain neuro-chip (an electrode array wired into the neurons) chip records neural signals from the part of the brain that controls movement.

The chip then processes those signals, sending precise messages to wires implanted in different muscles of the patient's arm or hand, triggering the paralysed limb to grab a glass or scratch the nose.

"Our ultimate goal is for a person to think and effortlessly move the arm," Robert Kirsch, associate director of the Functional Electrical Stimulation Centre said.

The Spinal Cord Barrier

Whenever the spinal cord is damaged, or a neurodegenerative disease takes hold, neural circuits between the brain and the body break down, and communication between body and brain fails. The problem is, recreating spinal ganglia has been beyond our technology, as there are just so many of them.

We are just beginning to move into a realm where this is no longer the case.

In functional electrical stimulation (FES), electrical current is applied to specific nerves or muscles to trigger muscle contractions. The subject is asked to make a pre-designated movement of the limb being examined to map FES, such as a flick of the wrist, or curling the fingers, or bending the elbow, they trigger the nerve stimulation of the relevant muscles, allowing researchers to map the electrical patterns required.

When FES mappings are applied in the same patterns in an actual patient, the appropriate muscles obediently respond, moving the limb in the precise way desired.

Devices that can restore hand function and bladder control to some paralysis patients have already been approved by the US Gov., for use.

In a FES system Kirsch and his colleagues are testing for people with spinal-cord injuries severe enough to render them paralysed from the neck down, a pacemaker-like stimulator is surgically implanted in the patient's chest or abdomen, with connecting wires implanted in up to 12 different muscles. Another set of wires records activity in muscles that are under the patient's voluntary control. These signals are then used to trigger activity in the paralysed muscles.

This is all well and good for minor injuries, but, for complete paralysis, or for use with prosthetic limbs, sending the signals directly from the brain is the only way to go.

Enter a familiar name: CyberKinetics. Their flagship neuro-chip, the BrainGate, has proven itself remarkably good at picking up and transmitting signals from the brain to an external device.

Experts have high hopes for the new device. "We consider this the only current viable technology on the horizon to provide patients with high levels of cervical injury restoration and control of their limbs," says Joseph Pancrazio, director of the neural-engineering and neuroprosthesis research program at the National Institutes of Neurological Disorders and Stroke, one of the agencies funding the research.

Major Hurdles

There are of course, still severe hurdles to overcome.

BrainGate and its brethren are still wired in - a cable comes out of the skull. One of the key developments needed is a wireless system, which can communicate with a computer system without open wounds in the skull offering an all you can eat buffet to infection.

Implanted neuro-chips lose signal strength over time. The cause is still unknown, but over many months the signal strength ebbs away at the original implant site.

Interoperating between devices that connect to the brain will slow to a crawl unless set of standards for their communication is hammered out, before development progresses too far.

Upcoming tests

In the first set of tests, slated to begin next month, patients implanted with the CyberKinetics chip will try to move a virtual arm, allowing researchers to study what level of control they could hope to achieve and to identify the muscles that need to be stimulated to elicit useful movements. Once researchers have built an implantable chip and have demonstrated that patients can sufficiently control a virtual arm, the team will start integrating the chip and the FES system.

In the long term, researchers will likely have to meld multiple devices. "To fully realise the potential of these systems, we need to think about not just a single FES system for upper limbs," Pancrazio said. "We need to think about a network of systems. The individual may need systems for ventilation, bladder control, and bowel control."

See the full Story via external site: www.medgadget.com

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