Neural 'extension cord' developed for brain implants
18:18 19 January 2007
NewScientist.com news service
A "data cable" made from stretched nerve cells could someday help connect computers to the human nervous system. The modified cells should form better connections with human tissue than the metal electrodes currently used for purposes such as remotely controlling prosthetics (see Brain implant enables mind over matter).
"The nervous system doesn't like nasty hard metal or plastic," says Doug Smith, who is developing the cell-based cable at the University of Pennsylvania, US. Nerve tissue can develop scarring or shrink away from contact with metal and other non-biological materials, he says.
"Nerve cells will happily grow to form new connections with new nerve cells though," Smith adds, "we want to try that as an alternative to ramming something into a nerve or the brain. The idea is to make a kind of extension cord." Prototype cables developed by his team have already been shown to transmit simple signals effectively.
In 2001, Smith and colleagues developed a way to grow new lengths of nerve fibre by gradually pulling apart groups of connected neurons (see Nerve racking stuff). Lengths of nerve generated in this way, and measuring up to 10 centimetres, have already been used to fix damaged nerves in the limbs of human patients. Protein coating
The data cables are created in the same way. A group of neurons is cultured on top of an array of 96 electrodes covered with a protein coating that causes them to attach. When placed 100 microns (about the width of a human hair) from another patch of neurons on a separate plate, the cells grow towards them, eventually joining neuron clumps together.
A motor is then used to slowly draw the two plates apart – causing the nerve fibres to continuing growing, at up to 1 cm each day. "We plan to use the free end to interface with the nervous system," Smith told New Scientist
, "while the other end interfaces with a computer."
Tests have already shown that electrical signals can be transmitted in both directions along the cord. "Tests in animal models are next," says Smith. Connecting the chord to electrodes outside of the brain means the reaction of neurons to non-organic material can be controlled. In future, the cord could connect an amputee's nerves to a sophisticated prosthetic, he says, and might even offer a way to connect artificial eyes or ears to the brain. Thought control
Christopher James, who works on brain-computer interfaces at Southampton University, UK, gives the work a cautious welcome. "This approach does sound like a good idea," he says. "Although directly attaching electrodes to the brain has been shown to work, the long term effects are not known."
But James adds that, in the long run, it may not be necessary to interface directly with nerves at all. "In Europe most researchers in this field are using non-invasive EEG," he explains (see 'Mental typewriter' controlled by thought alone).
"The signals are weaker so more complex processing is needed, but not having to perform surgery on the nervous system has many advantages," James says.