Chemical Coding of Behavior in the Brain

Distinctive patterns of behavior can be elicited by directly stimulating the brain with substances that are normally found in it, or with synthetic compounds resembling these substances. Recent research shows that the response elicited depends on both the site stimulated and the type of chemical used. Compounds of different classes, applied via the same cannula to exactly the same site in the brain, can elicit different kinds of behavior, or opposite effects on the same kind of behavior. This differential sensitivity is useful in tracing the circuits in the brain that control different types of behavior, especially since some of these circuits are intimately interlaced in certain places. A better understanding of the chemical coding of behavioral systems in the brain may also help ultimately to provide a more rational foundation for the discovery of new drugs to treat certain forms of mental disorder.