Placebo expectancy effects in the relationship between glucose and cognition

Area of Science:

• Cognitive Neuroscience
• Human Physiology
• Nutritional Psychology

Background:

• Glucose is often studied for its effects on cognitive function.
• Previous research has yielded mixed results regarding glucose's impact on cognition.
• The role of participant expectancy in these effects remains unclear.

Purpose of the Study:

• To investigate the influence of expectancy on glucose's effects on cognitive performance.
• To examine how informed versus misinformed expectations affect cognitive tasks after glucose or aspartame consumption.
• To clarify the relationship between glucose, expectancy, and specific cognitive domains.

Main Methods:

• A balanced placebo design with 26 participants in a within-subjects study.
• Four counterbalanced experimental sessions involving drinks with glucose or aspartame, with accurate or inaccurate labeling.
• Cognitive assessment battery including vigilance, verbal recall, recognition memory, and motor speed, alongside blood glucose and mood monitoring.

Main Results:

• Glucose improved recognition memory times, contrary to prior literature.
• Performance on the Bakan vigilance task improved with glucose, but only when participants expected it.
• No significant effects of drink type or expectancy were observed on other cognitive measures.

Conclusions:

• Participant expectancy significantly modulates the cognitive benefits of glucose, particularly for vigilance tasks.
• The findings suggest that expectancy, not just glucose itself, contributes to observed cognitive enhancements.
• Future research should consider expectancy effects when using equi-sweet controls like aspartame in cognitive studies.