For years, futurists have dreamed of machines that could translate pure thought into action. Now, human trials are set to begin on an interface involving chips implanted in the brain that one day might enable students with severe disabilities to communicate effectively and even learn in a traditional classroom setting.

Cyberkinetics Inc. of Foxboro, Mass., has received approval from the Food and Drug Administration to begin a clinical trial in which four-square-millimeter chips will be placed beneath the skulls of paralyzed patients.

If successful, the chips could allow patients to command a computer to act--merely by thinking about the instructions they wish to send.

It's a small, early step in a mission to improve the quality of life for victims of strokes and debilitating diseases such as cerebral palsy or Lou Gehrig's disease (amyotrophic lateral sclerosis). Many victims of such ailments now can survive for long periods thanks to life support, but their quality of life is poor.

"A computer is a gateway to everything else these patients would like to do, including motivating your own muscles through electrical stimulation," said Cyberkinetics chief executive Tim Surgenor. "This is a step in the process."

The company is far from the only research group active in the field. An Atlanta company, Neural Signals, has conducted six similar implants as part of a clinical trial and hopes to conduct more. But for now, its device contains relatively simple electrodes, and experts say Cyberkinetics will be the first to engage in a long-term, human trial with a more sophisticated device placed inside a patient's brain. It hopes to bring a product to market in three to five years.

A number of research groups have focused on brain-computer links in recent years.

In 1998, Neural Signals researchers said a brain implant let a paralyzed stroke victim move a cursor to point out phrases like "See you later. Nice talking with you" on a computer screen. The next year, other scientists said electrodes on the scalp of two Lou Gehrig's disease patients let them spell messages on a computer screen.

Cyberkinetics founder John Donoghue, a Brown University neuroscientist, attracted attention with research on monkeys that was published in 2002 in the journal Nature.

Three rhesus monkeys were given implants, which were first used to record signals from their motor cortex--an area of the brain that controls movement--as they manipulated a joystick with their hands. Those signals were then used to develop a program that enabled one of the monkeys to continue moving a computer cursor with its brain.

The idea is not to stimulate the mind, but rather to map neural activity so as to discern when the brain is signaling a desire to make a particular physical movement.