McComb, M. M., Code, R. A., Merrick, J. M. et al. 2012. Assessment of the reinforcing potential of auditory enrichment in adult male rhesus macaques. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 640 (Abstract #PS48).

Environmental enrichment is a concept that describes how the environment of captive animals can be changed for the benefit of the inhabitants. In 2000, Wright and colleagues suggested that tonal melodies form musical gestalts for monkeys, as they do for humans. However, McDermott and Hauser have shown that tamarins preferred silence to music in a free-choice split maze procedure. The present study examined free-choice selection of auditory enrichment in adult male rhesus monkeys. Each monkey was given access to turn-on or turn-off 2 musical/auditory selections in a standard 2-lever operant procedure. Auditory recordings were presented through an external speaker and monkeys were free to choose to turn-on standard recordings of classic orchestra music or rainforest sounds. Sessions were 3 h in duration. Each session was subdivided into 3 1-h recording periods with 15 min between each period and the pattern of responding on each of 2 levers was recorded. Responses on one lever activated music presentation and responses on the alternate lever would turn off the music. To assess the relative primary reinforcing properties of the music a third test session was conducted in which nonfood deprived monkeys could earn a single food pellet for responses on a lever. All animals extinguished lever press responding for music presentation by the second or third hour of the test session for both auditory selections; thus, they did not initiate or maintain robust responding on the lever for their free-choice delivery. In contrast, nonfood deprived monkeys responded throughout the sessions for food deliveries. These data suggest that auditory enrichment presentation is not a robust primary reinforcer in rhesus monkeys in a free-choice operant lever-press response assay. In contrast food presentation did initiate and maintain lever press responding, even in a food satiated state. These data suggest that environmental musical enrichment is not a primary reinforcer in laboratory rhesus monkeys and does not support a claim that musical enrichment will enhance species-specific behaviors.