Constraints on decay of environmental sound memory in adult rats.

When adult rats are pretreated with a 48-h-long 'repetitive nonreinforced sound exposure', performance in two-sound discriminative operant conditioning transiently improves. We have already proven that this 'sound exposure-enhanced discrimination' is dependent upon enhancement of the perceptual capacity of the auditory cortex. This study investigated principles governing decay of sound exposure-enhanced discrimination decay. Sound exposure-enhanced discrimination disappeared within approximately 72 h if animals were deprived of environmental sounds after sound exposure, and that shortened to less than approximately 60 h if they were exposed to environmental sounds in the animal room. Sound-deprivation itself exerted no clear effects. These findings suggest that the memory of a passively exposed behaviorally irrelevant sound signal does not merely pass along the intrinsic lifetime but also gets deteriorated by other incoming signals.