Glucose facilitation of cognitive performance in healthy young adults:: examination of the influence of fast-duration, time of day and pre-consumption plasma glucose levels

Rationale: Previous investigations have demonstrated increased performance after the administration of a glucose-load on certain aspects of cognitive functioning in healthy young adults. Generally these studies have used a procedure where participants were tested in the morning after an overnight fast. Objective: The aim of the present study was, for the first time, to investigate the glucose cognitive facilitation effect under more natural testing times and with shorter duration of the previous fast. Methods: Measures of verbal and non-verbal memory performance were compared under different fasting intervals (2-h fast versus overnight fast), times (morning versus afternoon) and glycaemic conditions (glucose versus aspartame drinks) in healthy young participants. Results: There was a significant glucose facilitation effect on long-term verbal memory performance. In addition, glucose significantly enhanced long-term spatial memory performance. The effect of glucose was essentially equivalent whether it was given after an overnight fast or a 2-h fast following breakfast or lunch. There was no effect of drink and time of day on working memory performance. Conclusions: The results of this study further support the hypothesis that glucose administration can enhance certain aspects of memory performance in healthy young adults. More significantly, the findings indicate that this cognitive facilitation effect persists under more naturalistic conditions of glucose administration and is not restricted to long fast durations or morning administration.