Behavioral methods for measuring effects of drugs on learning and memory in animals

This review describes methods for measuring effects of drugs on learning and memory in animals, proceeding from relatively simple nonassociative learning (habituation) to classical and instrumental conditioning, and concluding with complex measures for measuring learning and memory repeatedly in the individual animal. Procedures for separating drug effects specific to learning and memory from non-specific effects on activity, motivation, sensory and motor capacity, etc., were emphasized. For each method, selected experimental examples were presented which described the action of drugs on learning and memory, elucidated the behavioral processes involved in the drug effects, or illustrated methodological points. The various procedures used to measure drug effects on learning and memory in animals have yielded a bewildering array of often-contradictory results. Quantitative differences in effectiveness of drugs in the different procedures are common. Drugs (for example, the nootropics) that alter learning or memory in a few procedures may be totally without activity in many others. How are these discrepancies to be interpreted? The apparent inconsistencies in the data can, for the most part, be understood in terms of the nature of learning and memory. "Learning" and "memory" are hypothetical processes presumed to underlie enduring changes in behavior resulting from the organism's interaction with environmental stimuli. Given such a broad definition, the prevalence of inconsistencies in the data is hardly surprising. It is unlikely that the same mechanisms should underlie all of the wide variety of behavioral changes included under the rubrics "learning" or "memory." (For a contrary view, based on consistencies among results obtained in the diverse procedures, see Zornetzer). How, then, should drug effects on learning and memory be identified or measured? The first step, of course, is to rule out those drug effects that do not conform to the definition of learning or memory. This review has described strategies and procedures by which this can be accomplished. However, even when this is done there is no single procedure that can detect drug effects on learning and memory in general, nor, in view of the heterogeneous behaviors involved, is it likely that such a universal procedure will ever be found. Thus, a multi-faceted strategy will be required. Some of the simpler procedures described in this review may be adequate for the initial identification of interest