The scientists derived their findings by studying monkeys that had been trained to make precise arm movements. The monkeys were taught to pause briefly before making the reach, thus letting their brain prepare for a moment before moving.
Remember, the goal was to help build brain-controlled prostheses. Because the neurons in the brain always send out signals, engineers must be able to differentiate the command to act from the signals that accompany preparation.
To understand how this worked with the monkey's arm, the scientists took electrical readings at three places during the experiments: from the arm muscles, and from each of two motor cortical regions in the brain known to control arm movements.
The muscle readings enabled the scientists to ascertain what sorts of signals the arm receives during the preparatory state compared with the action step.
The brain readings were more complex.
Two regions control arm movements. They are located near the top center of the brain, an inch to the side.
Each of the two regions is made up of more than 20 million neurons. The scientists wanted to understand the behavior of both regions, but they couldn't probe millions of neurons. So they took readings from carefully chosen samples of about 100 to 200 individual neurons in each of the two regions.
During experiments the scientists examined the monkeys' brain readings at two levels.
On one level, they considered the activity of individual neurons how quickly or slowly the neurons fired signals.
At a higher level, the scientists also identified patterns of changes in the activity of many neurons. This is a relatively new technique for neuroscience, called a population and dimensionality analysis. Its goal is to understand how neurons work
|Contact: Tom Abate|
Stanford School of Engineering