Intensity expectation modifies gustatory evoked potentials to sweet taste: Evidence of bidirectional assimilation in early perceptual processing.

Expectations can affect subjective sensory and hedonic ratings of tastes, but it is unclear whether they also shape sensory experience at a perceptual level. The neural correlates of the taste-expectancy relationship were explored through EEG analysis. Using a trial-by-trial cueing paradigm, lingual delivery of 0.05 M or 0.3 M sucrose solutions was preceded by congruent or incongruent visual cues designed to promote anticipation of either a low-sweet or high-sweet solution. When participants were cued to expect low-sweet, but received high-sweet (incongruent cue), intensity ratings for high-sweet decreased. Likewise, expectation of high-sweet increased intensity ratings of low-sweet solutions. Taste-dependent, right central-parietal gustatory ERPs were detected, with greater P1 (associated with greater right insula activation) and P2 peak amplitudes for high-sweet tastes. Valid cue-taste pairings led to specific reduced right-lateralized N400 responses (associated with an attenuation in right insula activation) compared with invalid cue-taste pairings. Finally, P1 amplitudes following invalidly cued low-sweet tastes closely matched those generated by expected high-sweet tastes, and P1 amplitudes for invalidly cued high-sweet tastes resembled those generated by low-sweet tastes. We conclude that, as well as modifying subjective ratings toward the anticipated intensity level, expectations affect cortical activity in a top-down manner to induce bidirectional assimilation in the early perceptual processing of sweet taste and modulate N400 ERP components not previously associated with gustatory stimulation.