The impact of glucose and glucose expectancy effects on cognitive performance

Glucose is thought to facilitate cognition, particularly memory, but there is evidence that glucose effects may be influenced by drink expectancy. This study examined the joint impact of glucose and glucose expectancy on memory and other cognitive processes. Ninety-three fasted participants were allocated to one of six groups defined by two independent factors: drink given (glucose/placebo) and drink expected (glucose/placebo/ unspecified). Self-reported stress and arousal were rated at pre-drink and post-test intervals. Ten minutes after the drink, computer tasks from the ACT system assessed delayed free recall, location recognition, and semantic categorization followed an immediate free recall component. The results showed no significant effects of drink or expectancy on stress or arousal. Delayed free-recall, location recognition, semantic categorization and immediate free-recall showed the expected effects of internal task manipulations, but in none of the tests was there any evidence of significant beneficial effects of glucose or other impact of glucose or drink expectancy. This is consistent with other work failing to find glucose effects on memory tasks (Azari, 1991.Psychopharmacology, 105(4):P.173-179) and provide evidence that expectancy effects are not responsible for earlier findings of a positive impact of glucose on memory ability.