Effect of amphetamine on long-term retention of verbal material.

A series of five experiments was conducted to investigate the temporal aspects of human memory consolidation of symbolic material through the administration of amphetamine. Subjects had to recall or recognise unrelated words from a previously presented list. The first experiments support the conjecture, based on animal studies, that amphetamine enhances long-term memory performance. Subsequently, enhancement is demonstrated with oral administration before learning, as well as with intramuscular injection after learning. It is shown that improved recall cannot be explained solely by general arousal or attentional processes, but must be due to consolidation. By introducing different test delays we show that consolidation of symbolic material can be modulated by amphetamine during the 1st hour after learning. In a final experiment we demonstrate that the memory enhancement applies to recall as well as to recognition. The implications of the present results are discussed in the context of recent research on LTP processes.