In our present technological environment, we are used to the idea that machines can be controlled from a distance by means of radio signals. The doors of a garage can be opened or closed by pushing a button in our car; the channels and volume of a television set can be adjusted by pressing the corresponding knobs of a small telecommand instrument without moving from a comfortable armchair; and even orbiting capsules can now be directed from tracking stations on earth. These accomplishments should familiarize us with the idea that we may also control the biological functions of living organisms from a distance. Cats, monkeys, or human beings can be induced to flex a limb, to reject food, or to feel emotional excitement under the influence of electrical impulses reaching the depths of their brains through radio waves purposefully sent by an investigator.

This reality has introduced a variety of scientific and philosophical questions, and to understand the significance, potentials, and limitations of brain control, it is convenient to review briefly the basis for normal behavioral activity and the methodology for its possible artificial modification, and then to consider some representative examples of electrical control of behavior in both animals and man.