Primary Sources

Brain Signals Shown to Move a Robot's Arm

By SANDRA BLAKESLEE

Scientists have identified the signals generated in monkeys' brains as they prepare to move their arms, and, in a major step toward melding minds and machines, the researchers have now used those signals to move a robotic arm.

Before the monkeys began to reach out to pick up a morsel of food, the robot was able to "read" their intentions and carry out the same complex movement.

The long-term goal of such experiments is to help paralyzed people by developing machines that operate on the basis of human thoughts alone, said Dr. Miguel A. L. Nicolelis, a neuroscientist at Duke University, who led the team that carried out the new research, which is described in today's issue of the journal Nature.

Making a robot move in real time based on the activity of many brain cells in primates is "an important step" in developing neural prostheses, said Dr. Richard A. Andersen, a neuroscientist at the California Institute of Technology in Pasadena who does similar research. In most previous experiments, Dr. Andersen said, brain signals were fed into machines some time after the signals were obtained from animals.

But Dr. Andrew Schwartz, a senior fellow at the Neurosciences Institute in San Diego, who also works on the problem, cautioned, "We're not there yet."

Dr. Schwartz said it would take many years to engineer safe versions of personal robotic devices.

Still, researchers said that the research reported today was a major step forward.

The race to develop machines that can read the human mind began more than 30 years ago when scientists first put single electrodes into the brains of monkeys. To their great surprise, they found that some cells in areas that control movement start firing well before an animal begins to move. Eventually, they discovered that these areas are active because the brain literally plans voluntary movements before it carries them out. Moreover, such planning is not open to conscious perception.

Dr. Nicolelis offered this example: If someone moves to push open a heavy door, the brain generates signals telling the arms and legs exactly how much pressure to expect and how to maintain balance. The plan, based on previous experiences with heavy doors, is made a half-second before commands are sent down the spinal cord and out to muscles and joints where the movement is carried out, he said.

People whose spinal cords no longer carry signals down to their limbs may still be able to complete the planning phase in the brain, Dr. Nicolelis said, and it is this activity that researchers hope to capitalize on.

Dr. Eberhard Fetz, a neuroscientist at the University of Washington, said scientists had made many recordings from single cells and small groups of cells and used them to run robots, but not in real time and not for complex movements. In related research, a handful of paralyzed patients have been taught to use their own brain signals, measured from both inside and outside the skull, to move a computer cursor. But they are not using these signals to move entire limbs, Dr. Fetz said, and their efforts are laborious.

In the new experiments, scientists inserted hair-thin electrodes into the brains of two owl monkeys. One had 96 electrodes and the other had 32 electrodes spread over three brain areas involved in planning movements. Over the next two years as the monkeys carried out movements, the researchers collected brain signals — measured as changes in firing rates — from hundreds of cells that came into contact with the electrodes. The researchers were looking for specific brain patterns generated when planning complex voluntary movements.

For example, in one task the animals used a joy stick to move an object to the left or right, and their brain signals were recorded. In a second task, animals sat before a square tray and looked for a piece of food set in any one of the four corners. Again, their brain signals were recorded as they mentally planned where to reach their arms to get the food and bring it to their mouths.

Using advanced computational techniques, the researchers identified patterns used to plan the reaching movements and transformed those patterns into numerical instructions that could operate a robot.

"As the monkey brain prepares the pattern required to make the movement, we record it and send the signal to a computer," Dr. Nicolelis said. "As the monkey starts to move, our prediction is sent to the robot, and it moves at the same time."

The researchers also sent the monkeys' brain signals over the Internet to another robot arm at the Massachusetts Institute of Technology.

The next step will be to "close the loop," Dr. Andersen said. With visual and perhaps tactile feedback from the robot, the monkey might not bother to reach with its own arm anymore. It would merely think about making the movement and let the robot do the work.

If these experiments continue to advance, people may one day learn to represent prosthetic tools as extensions of their own bodies, Dr. Fetz said. But many big hurdles remain, including how to miniaturize electrodes and implant them safely, and practical devices are a long way off.

Source

The New Yorks Times, November 16, 2000