The Physiological And Neural Mechanisms Of The Cue Reactivity In Spicy Food Cravers

“Food craving” refers to “a strong desire to consume a specific food(or type of food)that is hard to resist”.Food cravers are those who have strong desires to consume a specific food(or type of food).Numerous studies have shown that food cravers exhibit strong cue reactivity such as physiological and behavioral response,and brain activities when exposed to specific food cues.These responses are called “craving response”,or “cue-induced craving”.So far,studies on food craving mainly focus on sweet food craving,such as chocolate craving.A survey investigating eating habit among 500,000 Chinese people showed that more than 30% adults consume spicy food every day,with large geographic diversity.People from Southwest of China consume spicy food most frequently nationwide.The phenomenon and mechanism of “spicy food craving” is worthy of investigation because of its unique geographical and cultural features,and close relationship with public health issues.However,there’s no study on spicy food craving so far.Therefore,this study explored the issue on “the cue reactivity of spicy food cravers”.We firstly designed the Spicy Food Craving Questionnaire,and then explored the cue reactivity among spicy food cravers by means of biofeedback technology and f MRI.At the same time,the resting state f MRI revealed the intrinsic mechanism of spicy food craving.Study one consists of two studies.Based on Food Craving Questionnaire-Trait-reduced and its revelant researches,study 1 developed the Spciy Food Craving Questionnaire(SFCQ).After open questionnaire survey,initial questionnaire preparation,exploratory and confirmatory factor analysis,the final SFCQ consisted of two factors.The first one is “behavior and positive reinforcement”,and the second is “cognition and thoughts”.The questionnaire has good reliability and validity and can be used as a preliminary measurement tool for the study on spicy food craving.In study 2,based on the Chinese dietary characteristics,we selected and assessed the spicy foods and matched non-spicy foods needed for the study to provide the basis for follow-up studies.The two types of pictures after standardization and assessment have no significant differences in the dimensions of deliciousness,pleasure,familiarity,etc.,but have significant differences in the degree of pungency.There are high degree of internal consistency in all dimensions.In study two,we explored the real spicy food cue-induced reactivity in spicy food cravers by means of biofeedback technology.Study 3 investigated cue-induced physiological responses such as salivation,heart rate,skin temprature,and skin conduction.Results revealed that salivation and heart rate increased significantly in spicy food cravers when exposed to spicy food cues,and both were larger than non-cravers.This indicated that salivation and heart rate may both reflect the subjective craving of cravers.Study 4 explored the cue-induced eating behavior among spicy food cravers.Results showed that spicy food exposure elicited significantly more spicy food comsuption in craver,while there was no cue-induced intake among non-cravers.Furthermore,study 5 investigated the relationship between cue-induced subjective craving,physiological responses and spicy food intake.Results showed that heart rate during spicy food exposure was positively related to increase in subjective spicy food craving,changes in subjective spicy food craving during exposure could significantly predict spicy food consuption.That is,the more the subjective craving increased,the more spicy food consumed.In general,study two validated the cue reactivity theory and cue-induce overeating model.In study three,we examined the spicy food cue-induced brain response pattern using by means of two brain imaging studies.Study 6 used an adapted Stroop paradigm.The results showed that for the "spicy vs.Non-spicy" contrast,the cravers had significantly more activation in the right cerebellum and left orbitofrontal cortex than non-cravers.Correlation analysis found that among spicy food cravers,the reaction time to spicy food cues was positively correlated with the percent signal change of the orbitofrontal cortex.This may indicate that spicy food cravers had more automatic representation and coding of conditioned spicy cues,and there was bottom-up processing of reward information brought by spicy food cues.Therefore,they needed more time to disengage from the spicy food cues to complete the experimental task.Study 7 employed an cue-reactivity paradigm and found that spicy food cravers exhibited increased brain activation in bilateral insula,left putamen,left dorsal ACC,right inferior parietal lobule,right lingual gyrus,bilateral cuneus,left precuneus,left fusiform gyrus,and right precentral gyrus compared to non-cravers when exposed to spicy food cues.Percent signal changes within the right insula,left putamen,and left d ACC were positively associated with subjective spicy food craving during the scan among cravers.Moreover,percent signal change within right inferior parietal lobule was significantly correlated with the frequency of spicy food intake among cravers.In total,study three demonstrated that spicy food cues and other reinforcements cues shared the common neural mechanisms involved in reward,motivation,affective response and habit formation,and these brain activites were correlated with subjective craving and craving-related behavior.Based on study 7,study four(study 8)explored the differences of resting state whole-brain functional connectivity with insula as seeds between spicy food cravers and non-cravers.In addition,we investigated the correlation between fuctional connectivity,spicy food craving score,and trait impulsivity.Results showed that:(1)the strength of functional connectivity between insula and occipital gyrus was significantly higher in cravers than non-cravers,(2)the strength of functional connectivity between insula and occipital gyrus,spicy food craving score,and Barratt Impulsivity Scale-motor impulsivity were correlated with each other significantly.Mediation analysis indicated that insula-occipital functional connectivity could be the mediating factor between motor impulsivity and spicy food craving score.Therefore we speculate that spicy food cravers may have a higher degree of exteroception,and they may be more sensitive to arousing visual and motor stimuli.According to the results of mediation analysis,on one hand,motor impulsivity had direct effect on spicy food craving,that is,individuals with higher motor impulsivity may experience more spicy food craving;on the other hand,motor impulsivity impacts spicy food craving through the role of insula-occipital functional connectivity.Study four revealed the intrinsic mechanism of spicy food craving to some degree.From the studies above,we also found that the score of external eating was higher in spicy food cravers than non-craver,and the score of perceived self-regulatory success was much lower in cravers than non-cravers.Together with finding of study four,we conducted the following studies to inspect the inhibition control of food cravers.Study 9 adopted the event-related potentials to explore the general and food-related inhibitory control in spicy food cravers.Results showed that spicy food cravers did not differ from non-cravers in general inhibitory control,but had a significantly lower spicy food-related no-go P3 than non-craver.This may indicate that they had poor ability in inhibiting responses to spicy food cues.Furthermore,we extend our subjects to restrained eaters,those who have a high degree of trait food craving and cue reactivity,but have a higher risk to develop into eating disorders.We examined food-related inhibitory control before and after food exposure among restrained and unrestrained eaters,and the relationship with cue-induced food craving.Results showed that high-trait food-craving restraind eaters exhibited significantly increased food-related no-go P3 after food exposure.In addition,the no-go P3 amplitude was marginally positively correlated with cue-induced food desire in restrained eaters.Study five demonstrated that spicy food cravers were worse at inhibiting spicy food-related responses.Larger no-go P3 after food exposure in restrained eaters may indicate the increased subjective food cue reactivity.In conclusion,spicy food cravers may have heightened cue reactivity to spicy food cues,as reflected by the increased physiological response and brain activities involved in reward,motivation and affective response.Meanwhile,we also found the resting state pattern and personality trait related to spicy food cravving.For the first time,this study carried out an exploratory study on the phenomenon of “craving for spicy food”,verified the cue reactivity theory,and to some extent revealed the physiology and neural mechanism of spicy food craving,which has theoretical innovation value.