Glucose, relational memory, and the hippocampus

Rationale
Many studies suggest glucose can temporarily enhance hippocampal dependent memories. As the hippocampus plays a key role in associative learning, we examined the influence of glucose on verbal paired associate memory.

Objective
This study examines how glucose modifies performance on a relational memory task by examining its influence on learning, subsequent forgetting, and relearning.

Methods
A selective reminding procedure was used to show high and low imagability paired associates to 80 participants, who were seen twice. On the first session they received 25g glucose pre-learning, 25g glucose post-learning, or placebo. On the second session, one week later, they received 25g glucose or placebo. Cued-recall was evaluated after each learning trial, one week later to assess forgetting and after an opportunity to relearn the material forgotten.

Results
Glucose did not influence paired associate acquisition. Those given glucose pre-learning tended to forget less material the following week and, independently, glucose at retrieval facilitated cued-recall. Both forms of facilitation were equally apparent on low and high imagability pairs. The benefit of glucose pre-learning was eliminated once the paired associates had been seen again, but the benefit of glucose at retrieval extended into the second re-learning trial.

Conclusions
The discussion considers the cognitive processes and hippocampal basis for paired associate learning and retention, and the implications for glucose’s mode of action. It is proposed that glucose during encoding serves to make the delayed memories initially more available, whereas its influence during delayed retrieval makes available memories temporary more accessible.