Effects of aging on the acquisition and extinction of excitatory conditioning in Drosophila melanogaster

Young (7-day-old), middle-aged (28-day-old), and old (49-day-old) Drosophila melanogaster were compared for acquisition, then extinction, of excitatory conditioning of the Proboscis Extension Response. The contribution of nonassociative processes (sucrose-induced Central Excitatory State, Pseudoconditioning) in the elicitation of conditioned responses was simultaneously assessed. Old flies displayed a faster and stronger acquisition than middle-aged ones, whereas no significant acquisition was stated in young flies. The influence of nonassociative processes on the acquisition was of minor importance, even though Central Excitatory State increased with age. Old flies proved also to be the slowest to extinguish. Because nonassociative contamination was not involved during extinction, one may wonder whether extinction was delayed in old flies mainly due to a higher level of acquisition or to a behavioral rigidity. (C) 1999 Elsevier Science Inc.