Hebb proposed 50 years ago that animals perceive objects and carry out actions thanks to the collective activity of huge assemblies of brain cells. Since then, however, brain researchers have tended to focus on the responses of one or a few neurons at a time. Both indicate that human perception and learning arise from the synchronized activity of clusters of neurons. Large numbers of nerve cells may briefly align the peaks and valleys of their electrical outbursts in order to render unified scenes and meanings from diverse sensations. The new efforts rely instead on brain waves measured by electrodes placed on the scalp.
Brain waves arise from synchronized neural activity.
Of particular interest are gamma waves, which are the result of thousands of neurons emitting equivalent electrical signals around 40 times a second. They pressed one of two computer keys to indicate what they saw. Brain tissue involved in vision exhibited gamma activity for an instant when volunteers scrutinized faces but not when they viewed the shapes. These synchronized responses, which Varela's group considers crucial for integrating related sensations into a vision of someone's face, dissolved before any key was pressed. A second burst of gamma activity, which may have helped coordinate an appropriate reaction, arose in motor areas of the brain as participants pressed a key.