Habituation of facial muscle responses to repeated food stimuli

We have shown in a series of studies that the human salivary response habituates to repeated presentation of gustatory cues. Parallel animal research has shown that mouthing and food acceptance also habituate. Facial expressions represent a complex response pattern in animals and humans that may provide an objective measurement of motivation to eat. The current study assessed whether facial muscles (orbicularis oris region, risorius region, and zygomaticus region) that regulate mouthing habituate to repeated presentations of a small amount (3 kcal) of a pleasant tasting food stimulus. Participants were randomly assigned to groups that received ten presentations of the same or changing taste stimuli. Following these trials all subjects were presented a novel dishabituating stimulus followed by the habituating stimulus. Integrated facial electromyography EMG responses over each region were measured for a 50 second period following the taste stimulus. Results showed differential habituation rates across the two groups, with participants in the repeated taste group showing decreases in contrast to the changing taste group who did not decrease. The participants in the repeated taste group showed dishabituation of these responses. These results systematically replicate basic animal research, and extend the number of responses related to eating in humans that habituate to repeated food presentations.