The brave bull bore down on the unarmed matador" - a scientist who had never faced a fighting bull. But the charging animal's horns never reached the man behind the heavy red cape. Moments before that could happen, Dr. Jose M. R. Delgado, the scientist, pressed a button on a small radio transmitter in his hand, and the bull braked to a halt. Then, he pressed another button on the transmitter and the bull obediently turned to the right and trotted away. The bull was obeying commands from his brain that had been called forth by electrical stimulation-by the radio signals-of certain regions in which fine wire electrodes had been painlessly implanted the day before. [Experiments] have shown, he explained, that "functions traditionally related to the psyche, such as friendliness, pleasure or verbal expression, can be induced, modified and inhibited by direct electrical stimulation of the brain." For example, he has been able to "play" monkeys and cats 'like little electronic toys" that yawn, hide, fight, play, mate and go to sleep on command. With humans under treatment for epilepsy, he has increased word output sixfold in one person, has produced severe anxiety in another, and in several others has induced feelings of profound friendliness-all by electrical stimulation of various specific regions of their brains. "I do not know why more work of this sort isn't done," he remarked recently, "because it is so economical and easy." Monkeys will learn to press a button that sends a stimulus to the brain of an enraged member of the colony and calms it down, indicating that animals can be taught to control one another's behavior.