Learning performance of normal and mutant Drosophila after repeated conditioning trials with discrete stimuli

A new olfactory conditioning procedure is described using short training tr ials with discrete presentation of conditioned stimuli (CS) and uncondition ed stimuli (US). A short odor presentation along with a single-shock stimul us produced modest but reliable and reproducible learning. Multiple trials presented sequentially improved performance with increasing trial number. T rial spacing had a significant impact on performance. Two trials presented with a short intertrial interval (ITI) produced no improvement over a singl e trial; two trials with a 15 min ITI significantly boosted performance. Th is effect required two associative trials, because substituting one of the trials with the CS alone, US alone, or an unpaired CS-US failed to boost pe rformance. The increase in initial performance with two trials decayed with in 15 min after training. Thus, the effect is short-lived. The utility of u sing a battery of tests, including a single short trial, two massed trials, and two spaced trials, to investigate parameters of memory formation in se veral mutants was demonstrated.