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 Scientists Detail Latest Advances In Development Of Prosthetic Devices For Paralyzed

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Date posted: 31/10/2004

(Press Release) New research is speeding the development of brain-controlled devices that may soon allow amputees and paraplegics to use their limbs. Within a few short years, these so-called brain-computer interfaces (BCI) may also allow people completely paralyzed by neurodegenerative diseases to regain some movement or ability to communicate with those around them.

In recent work, scientists created a BCI that collects information from hundreds of thousands of brain cells at once. In other new work, researchers have used electrodes that do not penetrate the brain to record brain activity that can control a BCI. Swedish scientists have greatly refined a prosthetic hand. And other scientists have trained a monkey to use a robotic arm controlled by its own thoughts.

The first brain-controlled movement came several years ago, with patients moving objects in virtual reality. Now four groups of scientists have built upon the earlier studies to bring the field closer to prosthetic devices controlled by thought. ?We are rapidly approaching a milestone,? says Andrew Schwartz, PhD, of the University of Pittsburgh Department of Neurobiology, referring to his work with a new anthropomorphic robotic arm.

Neuronal activity measurements are used to control BCIs. They are recorded either from individual brain cells (called single-unit recording) or from the scalp using electroencephalography (EEG). The recorded brain signals are then used to control a physical or virtual device that carries out a task according to the user's intent.

Both methods have their advantages and drawbacks. Recording from inside the brain requires that electrodes be surgically implanted, carrying the risk of infection. Neural scarring around the electrodes can also build up over time and cloud the data used to control the device. EEG measurements, on the other hand, are safe, but yield a much 'fuzzier' signal. In addition, users typically have to be trained for prolonged periods to master this new skill.

Scientists are now working to develop techniques that combine the advantages of both methods yet reduce their downfalls. Scientists in the laboratory of Richard Andersen, PhD, of the California Institute of Technology have developed a method that collects local field potentials (LFPs).

Instead of recording from individual neurons, the researchers implanted electrodes that collect information from hundreds of thousands of brain cells at once. Neural scarring affects all chronically implanted electrodes over time. But because LFP signals are not dependent on one particular cell, the signal is not affected nearly as much as single-unit recordings are. ?Physically and informationally, LFPs fall between single-unit recordings and EEGs,? says Daniella Meeker, BA, one of the researchers.

The researchers implanted just one electrode in a macaque monkey to record LFPs in the parietal cortex in each of 24 experiments. The parietal cortex is a brain area just upstream of the motor cortex in planning movements.

The monkey was trained to plan its movements without actually executing them. In each experiment, the monkey prepared to make its movements while the researchers recorded the LFP from a single location. This activity pattern was then used to program the BCI. Next, the monkey controlled the BCI with its thought pattern to move a cursor to a desired location on a computer screen.

Although the monkey's performance was not as good as it would have been with single-unit recordings, performance improved with training over time. The group plans to extend the study to include multiple recording sites, and to combine LFP measures with single-unit recordings. ?By using signals from several different brain areas, we hope to optimize BCI control over time,? says Meeker.

In other work that seeks to combine the benefits of single-unit and EEG recordings, Gerwin Schalk, MS, a computer scientist at the Wadsworth Center of the New York State Department of Health, has literally gone halfway between the techniques to control a BCI.

Instead of recording activity from within the cortex or from the scalp, Schalk and his colleagues at Wadsworth and at Washington University in St. Louis recorded from the surface of the brain?inside the skull. This technique, called electrocorticographic (ECoG) recording, uses electrodes that do not penetrate the brain.

In earlier work, the group showed that humans could use ECoG recordings to control a cursor on a computer screen in one dimension, in an up-down motion. The current work extends this study to control movement in two dimensions. The researchers collected their data from an epileptic patient who was about to undergo therapeutic brain surgery. In routine preparation for the surgery, electrodes were implanted on the brain surface to monitor its activity.

The patient made movements?real and imagined?while the scientists recorded his brain activity and watched which signals changed during the tasks. The patient then fine-tuned these signals and used them to control a cursor on a computer screen using only his mind. It took only a few minutes of training to acquire this new skill?a vast improvement over the days or even weeks required to master an EEG-controlled BCI. ECoG recordings also have an advantage over single-neuron recording electrodes in that they are less invasive, and may carry fewer risks than those implanted into the brain.

?With a BCI controlled by ECoG signals, patients who have lost the ability to communicate could use a word processor, surf the Internet, or even control a prosthesis,? Schalk says. The group plans to extend their findings in more subjects, and hopes to develop a clinical device based on ECoG recordings.

New work from a group at Lund University in Sweden uses electromyography signals to improve hand and arm prostheses.

See the full Story via external site: apu.sfn.org

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