Inge Zeeuws, Natacha Deroost & Eric Soetens

1. NO INFLUENCE OF D-AMPHETAMINE ON CONSOLIDATION AND ABSTRACTION OF SEQUENCE KNOWLEDGE IN THE SRT TASK Email: Inge.Zeeuws@vub.ac.be This research was funded by the Research Department of the VUB Inge Zeeuws, Natacha Deroost & Eric Soetens Cognitive and Biological Psychology, Vrije Universiteit Brussel INTRODUCTION In previous research, it was found that d-amphetamine enhances the retention of explicitly learned verbal material by modulating consolidation. In this study, we investigated the influence of d-amphetamine on the consolidation of implicitly learned sequence knowledge acquired in a SRT task. Moreover, we examined whether consolidation of sequence knowledge involves the abstraction of the learned material. METHOD SRT task: participants respond to one of four horizonal locations of the stimulus. Sequence learning is inferred from a RT increase in a random block as compared to adjacent structured blocks. Two sessions on 2 subsequent days: each session: • Training phase: 15 blocks of 100 trials, Block 13 is random • Transfer phase: 4 blocks of 100 trials, Block18 is random Between-subjects: • Drug: 10 mg d-amphetamine and placebo • Condition: the sequence in the transfer phase was either the same, a mirror image of the training sequence or a different sequence structure RESULTS Sequence learning during training and transfer was observed for all conditions. However, sequence learning in the Same and Mirror condition was clearly more pronounced than in the Different condition. Importantly, no influence of d-amphetamine was found on sequence learning or on the consolidation of sequence knowledge. Figure 1: Mean RT’s for the Same condition. Training phase: d-amphetamine [F(1,47)=64,16; p<0.001] and placebo [F(1,47)=52,89; p<0.001]. Transfer phase: d-amphetamine [F(1,47)=65,90; p<0.001] and placebo [F(1,47)=62,69; p<0.001]. No drug influence during training [F(1,47)=0,01; ns] or transfer [F(1,47)=0,24; ns]. Figure 2: Mean RT’s for the Mirror condition. Training phase: d-amphetamine [F(1,47)=104,60; p<0.001] and placebo [F(1,47)=66,33; p<0.001]. Transfer phase: d-amphetamine [F(1,47)=33,19; p<0.001 and placebo [F(1,47)=30,05; p<0.001]. No drug influence during training [F(1,47)=3,29; ns] and transfer [F(1,47)=0,16; ns]. Fig 3: Mean RT’s for the Different condition. Training phase: d-amphetamine [F(1,47)=143,07 p<0.001] and placebo [F(1,47)=49,80; p<0.001]. Transfer phase: d-amphetamine [F(1,47)=5,70; p<0.05] and placebo [F(1,47)=5,47; p<0.05]. No drug influence during training [F(1,47)=0,7; ns] and transfer [F(1,47)=0,06; ns]. CONCLUSION Knowledge consolidation and abstraction are clearly both at play in implicit sequence learning. Although previous research revealed a positive effect of d-amphetamine on the retention of explicitly learned verbal material, no influence of the drug was found on the consolidation of implicitly learned sequence knowledge. This differential influence of d-amphetamine on the consolidation process indicates separate memory systems for implicit vs explicit leaning and verbal vs non-verbal material