The Cognitive And Neural Mechanisms Of Executive Function For Restrained Eaters

Dieting has become a very popular means of weight control among young women,irrespective of age,race,ethnicity and weight.According to recent reports,approximately 50% of the Western female population reports to be concerned with their weight,to be a regular dieter,or to attempt to limit food intake.Many people try to control their body weight by restricting their food intake,but most fail in the long-term.One group that seems particularly unsuccessful in controlling food intake is chronic dieters(i.e.,restrained eaters).Compared to unrestrained eaters,a high score on eating restraint is considered a risk factor for eating disorders or obesity.According to the report of WHO(World Health Organization),eating disorders is one main factor cases psychological problems for women,and also an important risk factor for the death of minors.Prior research in our laboratory used longitudinal design method(9,12,18,and 24 months follow-up)to examine the role of body dissatisfaction and social comparison on eating disorders.It was the first time to construct the influencing factors model of the eating disorder for Chinese adolescents.We found that restrained eating is the most common and the most critical factor in the process of eating disorders,which is also the key point from psychological problems turning to pathological behavior,and has a significant prediction effect on Chinese adolescents’ eating disorder.Moreover,executive functioning as a higher cognitive functions,mainly involved in the monitoring of individual cognition process,inhibiting irrelevant information,select input information,integrate information in long-term memory.It has been a hot research topic in the fields of neuroscience,cognitive psychology and cognitive neuroscience.So far,Pennington et al.generally accept a view on the division of executive function that it consists three components: inhibition of control,working memory and cognitive flexibility.Though a body of research indicated that the individual difference in executive functions such as inhibition control and working memory might significantly explain the reasons for diverse vulnerability of obesity and eating disorder,however,few researches systematically discussed the neural mechanism of restrained eater’s executive function.Existing research face a series of problems such as simplex in research content,controversial in conclusion and lack of standardization in participant selection and variable control.Various factors were found to cause such inconsistency.Such as participant selection(e.g.,different BMI,age and gender),paradigm(e.g.,Stop-Signal,Go-Nogo task),variable control(e.g.,emotional state,hunger)and stimuli selection(e.g.image,words and actual food).Existing evidences related to the executive function of restrained eaters have found to be controversial.Therefore,the present research aimed at systematically examine the neural mechanism of restrained eater’s executive function based upon 1 investigation and 6 fMRI studies.First(preparatory study),to confirm the validity and stability of the measurement,we recruited about 800 female college students to assess the score range,internal consistency coefficient and predictive validity of Restraint Scale,which served as the tool for participant selection(study 1)for latter studies.Results showed that the descriptive analysis resembles to the norm.Two subscales(concern of dieting,CD and weight fluctuation,WF)were showed good internal consistency.All subscales were significantly related to the body mass index(BMI),which demonstrated the good validity of the scale.Taken together,the Restraint Scale were show good application as a screening tool in the present research for participant selection.Second(feasibility),as a lack of fMRI study related to restrained eating,we tried to test whether the chosen stimuli(food image)could activate certain brain area and restrained eater’s vulnerability to these images.We observed 12 restrained eaters and 12 unrestrained eaters’ vulnerability toward food cues distinguished by calorie(study 2,oddball task).Result showed that compared with unrestrained eaters,restrained eaters had a faster reaction time toward high-calorie food cues.All participants showed a higher activation in areas related to reward,attention and visual process.Meanwhile,compared with neutral stimuli,when processing low-calorie food cues,they showed higher activation in vision-related area,that is,participants could distinguish different food cues with different calorie variance,and restrained eaters had a higher vulnerability toward food cues.Third,we examined restrained eater’s neural mechanism of inhibition control using word/food image Go-Nogo task(study 3,4).In the word Go-Nogo task,no significant difference was found between two groups on behavioral level.In neural mechanism level,however,compared with Go stimuli,No go stimuli induced a higher activation in middle frontal gyrus,inferior frontal gyrus,inferior temporal gyrus,frontal singulate gyrus,insula and visual cortex(e.g.,fusiform),indicating that the present study is validated in inducing participant’s behavioral inhibition control.No significant difference was found between restrained eaters and unrestrained eaters on general inhibition control ability in Nogo vs.Go condition.In the food-cue Go-Nogo task,results showed that when two groups reacted to high-calorie food stimuli in Go condition,there was found a marginal significant difference(p = 0.062),while restrained eaters had a faster reaction to high-calorie Go stimuli than unrestrained eaters.On the neural mechanism level,when exerting inhibition control to high-calorie food stimuli,restrained eaters had a higher activation in reward-related cortex such as parahippocampal gyrus,middle frontal gyrus,middle temporal gyrus and visual cortex;they also had a lower activation in inhibition-related cortex such as superior frontal gyrus and middle frontal gyrus.Results inciated that restrained eater’s high reward approaching and low inhibition control toward high-calorie food cues might increase the risk of weight gain and eating disorder.Forth,we examined restrained eater’s neural mechanism of working memory through 2 fMRI studies with word/food cue N-back task(study 5,6).In the word N-back task,results showed that participants had a longer reaction time in 2-back condition than 0-back condition and a higher false response rate.On the neural mechanism level,compared to the 0-back condition,when conducting 2-back task,participants had a higher activation in superior frontal gyrus,middle temporal gyrus and middle occipital gyrus,which indicated the monitor and update process to the information in working memory task.Similarly,in food-cue N-back task,the 2-back condition caused longer reaction time and higher false rate.Moreover,when in the high-calorie food cue condition,the reaction time and false rate seems even higher.Between group comparisons suggested that restrained eaters had a longer reaction time when determining high-calorie food cues.On the neural mechanism level compared to 0-back task,participants had a higher activation in superior frontal gyrus,middle frontal gyrus and superior temporal gyrus.In high-calorie food cue condition,restrained eater might have a high depletion of cognitive resource,which reflected in the higher activation in middle frontal gyrus.They tried to mobilize more frontal cortex to avoid the influence toward working memory.Finally,we used task switching paradigm to examine restrained eater’s neural mechanism of cognitive flexibility(study 7).Results showed that on the neural mechanism level,restrained eaters had a lower activation on middle frontal gyrus and precuneus,which may indicate the impaired cognitive flexibility of restrained eaters.Overall,the present research initially explored restrained eater’s executive control from three different phases--cognitive flexibility,working memory and inhibition control adopting neural imaging technology.Results suggested that the main difference between restrained eaters and unrestrained eaters appeared in the food cue processing.On the neural mechanism level,however,the differences between restrained eaters and unrestrained eaters were focused on frontal cortex such as superior frontal gyrus,middle frontal gyrus and limbic system such as insula and parahippocampal gyrus.These findings advanced our understanding to the question “why most restrained eaters fail”.In the meantime,they also shed light on future research aimed at applying pointed prevention and intervening practice toward restrained eating.We hope that the results will help early identification,and to reduce the potential social and economic costs.