Background: An improved long-term retention of verbal memory was observed after an acute D-amphetamine administration. It was proposed that D-amphetamine modulates consolidation, but a possible drug effect on retrieval could not be rejected.
Objectives: We want to provide additional support for the consolidation hypothesis, and investigate whether an influence on intervening retrieval can be refuted.
Methods: Thirty-six male paid volunteers participated in a double blind, counterbalanced, placebo-controlled design in which the number of intermediate free recall tests was manipulated.
Results: A significant D-amphetamine facilitation effect on recall performance emerged 1 h and 1 day after list learning. In line with the consolidation hypothesis, no effect was found on immediate tests. Importantly, the number of intermediate retrievals did not affect the magnitude of the drug effect, suggesting that the D-amphetamine facilitation effect is independent of retrieval.
Conclusion: The D-amphetamine facilitation effect on verbal memory does not involve a modulation of the initial encoding or short-term memory (STM) processes. Moreover, the drug does not enhance long-term retention by acting on intervening retrieval processes. The current findings are in line with the conjecture of an involvement of the consolidation process in the D-amphetamine facilitation effect on verbal memory in healthy humans.