Abstract
Previous studies suggest that oral glucose administration directly facilitates declarative memory encoding and retrieval (Sünram-Lea et al., 2002; Manning et al., 1992). However, glucose could indirectly facilitate memory encoding by already enhancing pre-mnemonic sensory or lexical/semantic processes, which produce important substrates for memory encoding. In the present study we used ERP measures combined with a robust placebo-controlled double-blind glucose elevation protocol to (1) replicate the glucose facilitation effect on declarative memory performance, and (2) determine whether glucose modulates pre-mnemonic or mnemonic processes at the encoding and retrieval stage. EEG was collected from 32 electrodes while participants performed a word recognition task under conditions of elevated (6.5 ± 0.12 mmol) and normal (4.57 ± 0.12 mmol) blood glucose levels. In line with the literature, recall rates were better in the glucose condition. Glucose also enlarged the LPC component, which is functionally linked to memory encoding and consolidation processes. Glucose also modulated VEPs (P1, N1), the P300, and the N400, a marker of pre-mnemonic lexical/semantic processing. The N400 amplitude positively correlated with memory performance. At the recognition stage similar effects on VEPs and the P300 were observed, and glucose numerically enhanced the FN400, while reducing the LP. In summary the glucose facilitation of declarative memory may be enacted through effects on earlier information processing stages as well as later memory-specific processes.