Environmental enrichment for nonhuman primates: theory and application.

Investigators have an obligation to promote the psychological well-being of nonhuman primates used in research. Considerable emphasis has been placed on providing nonhuman primates with enriched environments as a means to achieve this objective. A framework is provided that consists of a set of hypotheses about well-being, and the extent to which exposure to various enrichment devices and procedures actually promotes well-being is evaluated. Two hypotheses are concerned with fostering species-typical behavior: use (versus nonuse) of the enrichment, and whether use of enrichment helps normalize other aspects of the behavioral repertoire. Two additional hypotheses are concerned with abnormal behavior: whether currently existing enrichment lowers levels of abnormal behavior, and whether it prevents the behavior. This framework is applied to various enrichment strategies ranging from toys and foraging devices to social interaction. Most devices are used by nonhuman primates and thus constitute an important way to enrich the captive environment. However, enrichment devices vary as to their effectiveness in normalizing the behavioral repertoire and eliminating abnormal behavior. Only social contact satisfies the goal of promoting a wide variety of species-typical activities while at the same time reducing or preventing the development of abnormal behavior.