In 1954, Olds and Milner reported an observation that arguably represents the most intriguing and enigmatic phenomenon biopsychologists have yet encountered. They noted that a rat preferred the region of the test apparatus where it received electrical brain stimulation, and inferred that it might find the experience pleasurable. When the experimenters restructured their experimental paradigm to test this possibility, it was determined that the rat would learn and execute novel behaviors in order to obtain brief pulses of brain stimulation. Olds and Milner plausibly concluded that they had discovered brain mechanisms responsible for “reward.”
It is difficult to exaggerate the implications of this observation. Complex biological organisms could not have survived on earth had they not developed the ability to learn from experience – i.e., to repeat behaviors that have positive consequences such as finding food, water, or a mate, and to eliminate behaviors that have negative consequences such as exposure to predators, or extremes of heat or cold. Learning implies a fundamental reorganization of the relationship between the organism and its environment. Olds and Milner’s discovery promised insights into the basic neural mechanisms that are responsible for our capacity to achieve that reorganization.
Before we can meaningfully ask what has become of this promise, we must take a small detour into the domain of the philosopher. If we agree that the behavior of complex organisms is the result of learning, it follows that the conditions that promote learning are at the very heart of psychology. Philosophers have recognized this imperative by debating whether all behavior should be considered to be determined by a desire to maximize pleasure and minimize pain. A good many of them are uncomfortable with the implication of this dictum that humans might not exercise voluntary, discretionary control over their behavior. For some, this concern can be assuaged by definitions of reward and punishment that are expanded to include such acquired elements as satisfaction with one’s accomplishments and disappointment at one’s failures. Others will insist that humans are endowed with rational capabilities that can supersede the basic relationship between behavior and its consequences however broadly defined.
Related: José Delgado and Brainchips (PDF)