Scientists at Johns Hopkins University, using electrodes connected to a monkey's brain, say they have produced a computer image of the brain as it thinks.
''We have visualized a thought process, a mental transformation,'' said Dr. Apostolos Georgopoulos, a neuroscientist who led the research team. ''We've used a technique that lets a mental process be seen as a physical one.''
The team's study, published Friday in Science magazine, found that electrical activity among nerve cells of the motor cortex, the part of the brain that controls movement, can be tracked during the thinking that precedes purposeful movement. The finding might someday help scientists develop artificial limbs that respond electronically to the brain's instructions, Dr. Georgopoulos said. Anticipation of Tasks
Experiments on the subject, a trained rhesus monkey named Lambda, demonstrated that the electrical activity associated with mental calculations showed up on a computer screen thousandths of a second before the animal performed a task.
Dr. Georgopoulos has worked since 1980 to decipher the electrical brain activity that determines how an animal responds to stimulus, like a shining light.
''We know that the brain analyzes the situation and has to produce a movement that will be appropriate for the situation, with the appropriate direction in space,'' Dr. Georgopoulos said. ''So we ask the animal to make that movement, and we record the activity of the brain and see how the cells interrelate.''
Using a clock-like device with a circle of light bulbs, scientists taught Lambda to move a metal handle to a right angle to whichever light was turned on. Lambda, coaxed with rewards of banana juice, learned to respond correctly more than 80 percent of the time, Dr. Georgopoulos said.
Electrodes implanted into the monkey's cortex picked up the electrical activity of the cortical cells that control arm movement. The impulses were relayed to a computer and interpreted into images of vectors, or directional forces.
The computer graphics showed that milliseconds after the light flashed on, the electrical activity in those cells displayed a tendency to ''think'' in the direction of the light. The vectors then rotated in that direction.