Expectation Modulates Hedonic Experiences and Midbrain Responses to Sweet Flavor

Area of Science:

• Neuroscience
• Sensory Science
• Behavioral Science

Background:

• Non-nutritive sweeteners (NNS) are sugar substitutes used for weight management by reducing calorie intake.
• It is unclear if sugar and NNS elicit distinct brain responses or if expectations modulate these neural signals.
• Understanding these differences is crucial for dietary interventions and food choice behavior.

Purpose of the Study:

• To investigate whether sugar and NNS evoke different orosensory brain responses.
• To determine if neural responses to sweet flavors are modulated by expectancy.
• To link these findings to food choice behavior and dietary interventions.

Main Methods:

• fMRI scanning of 27 healthy adults who perceived sugar and NNS similarly.
• Administered sugar and artificially sweetened beverages under probabilistic and deterministic expectation paradigms.
• Manipulated participants' expectations of flavor delivery to assess neural and behavioral responses.

Main Results:

• Participant accuracy in distinguishing sugar from NNS depended on expectations.
• Expectations significantly altered the perceived pleasantness of both sugar and NNS.
• Expectation of sugar increased midbrain responses to NNS when sensory information was unreliable (deterministic task).

Conclusions:

• Expectancy plays a critical role in the behavioral and neural encoding of sweet flavors, especially with unreliable sensory input.
• The expectation of sugar enhances the subjective value of noncaloric sweeteners, potentially due to flavor-nutrient conditioning.
• These findings suggest that the rewarding effects of sugar may exceed those of NNS, influencing food choice behavior.