Social isolation blocks the expression of memory after training that a food is inedible in Aplysia fasciata.

Isolating a sexually mature Aplysia fasciata for either 1 or 24 hr immediately after training that a food is inedible blocks the subsequent expression of memory measured 24 hr later. Isolation that is delayed for 1 hr after training, but not for 12 hr after training, is also effective in blocking memory. Isolation affects memory because of a specific effect caused by the absence of pheromones secreted by conspecifics rather than by a nonspecific change in the chemical environment, because transferring animals to a novel environment (120% seawater) that contains a conspecific does not affect memory. Isolation also does not affect memory in sexually immature Aplysia, even though immature animals are able to sense one another's presence. Isolation may affect memory because social (and sexual) isolation is a form of stress in mature A. fasciata, and stress after training affects retention in many animals.