Temporal determinants of olfactory long-term retention in honeybee classical conditioning: nonmonotonous effects of the training trial interval.

The question of which acquisition parameters govern long-term retention is important to an understanding of memory function. We investigate the effects of the time interval between learning trials on mediate (1 day)- and long-term (4 days) retention. In classical conditioning of the proboscis extension reflex, we train honeybees to associate an odorant with a sucrose reward using intertrial intervals of either 30 s, 1 min, 3 min, or 20 min. Intervals of 20 and 1 min result in stable retention but 3-min and 30-s intervals result in reduced retention after 4 days compared to that seen after 1 day. Thus, stability of long-term retention depends nonmonotonously on the intertrial interval. Reduced retention with 3-min intervals might be caused by a disruption of memory consolidation which is known to be especially sensitive to interference 3 min after a conditioning trial. Habituation and backward inhibitory learning are discussed as explanations for reduced retention with 30-s intervals.