March 2005

Implanting Hope

Continued from page 2

By David Ewing Duncan

Reading Intent
Donoghue's work is best understood in the context of the scientific effort to interpret and act on neuronal activity. Some scientists, like Donoghue, want to implant electrodes to capture more neuronal data more quickly; others are not sure implants are necessary. But all share an interest in understanding how the brain might work with a computer to create practical technologies for a range of purposes.

The words of the neuronal language can be heard in the electrical "spikes" in neurons -- although some neuroscientists have proposed creating a BCI by monitoring broader, deeper "fields" of brain ac­tivity using electroencephalography, which would not require the surgical implantation of electrodes. EEG sensors have had some success, but they have produced only faint signals compared to implants that capture neuronal spikes.

A spike is the pinnacle of an electrical surge, the "action potential" that occurs when a neuron is activated and fires. On one of the monitors showing Nagle's brain activity, dozens of action potentials play out in rows across the screen as the computer compiles signals from the electrodes in Nagle's implant, each of which registers the activity of dozens of neurons. When a neuron fires, the line on the monitor begins to rise in proportion to the electrical surge, and then, moving at a speed more than 100 times faster than the blink of an eye, it peaks, which is what causes the "pop." Once the neuron has fired, its electrical signal drops back down, and the output either stays flat or begins its ascent again.

Neurons, when active, fire between 20 and 200 times a second. The timing and the location of spikes in the brain, and the interaction of multiple spikes among neurons, create the coherent signals that are turned into muscle movements and all the other "outputs" of the brain.

"Understanding how groupings of neurons work for motor activity is relatively simple," says Hatsopoulos, who helped write the algorithms for Braingate. "As we learn to read more neurons at once, it will eventually tell us how higher brain functions work, such as emotions and other behavior and thought processes."

By conducting human trials, Donoghue has pulled ahead of his colleagues, though other scientists have plans for their own clinical trials of neuro-prostheses controlled with implanted electrodes. In Atlanta, Kennedy's company has received approval from the FDA to test single- and double-electrode implants in severely disabled patients. At Caltech, Andersen's team has begun to experiment on humans suffering from epilepsy, using brain implants surgically embedded in the prefrontal cortex (an area that helps plan and execute bodily movement); the implants sense an oncoming seizure and apply tiny electrical shocks to shut it down. Though Andersen has no commercial plans for the device, he intends to expand the human tests in clinical trials.

Andersen is also expanding his work with monkeys; he has implanted sensors in the higher-functioning areas of a monkey's brain and deciphered some of the electrical signals whereby the monkey plans actions and others that seem to govern its motivation to perform a specific feat. "We have a difference in approach from Donoghue's work," says Andersen. "We're reading intent" -- whereas Donoghue is tapping into the motor-action part of the brain. Monkeys with electrodes in either brain region can move cursors and devices, says Andersen.

Duke's Nicolelis has invented a system that allows a monkey to move a prosthetic arm up and down to deliver a snack. Nicolelis also linked up his monkey's brain to the Internet and had the monkey operate a robot arm 950 kilometers away. He has been testing humans with deep brain implants to study the patterns in which their neurons fire when they squeeze balls. So far, he has recorded the output of up to 50 cells and is using this electrical data to devise algorithms to move a cursor. He is also studying how neurons in the brain adapt to the use of robotic arms and machines, since neurons are continually modified by the acquisition of new information and skills.

These types of experiments are rapidly advancing the technology, giving it more and more potential to help patients. At the University of Pittsburgh, Schwartz has run experiments enabling monkeys to move an artificial arm and hand more fluidly. "These devices have the degrees of motion of a human arm and elbow," he says. His team wants to test their arm on humans. "We're on a five-year horizon," Schwartz says, for the arm to be working well in humans.