Behavior And Resting State MRI Study Of The Effect Of Exercise On Children's Executive Function

Executive function is a top-down cognitive process that requires concentration and cannot be completed by automatic processing or relying on instinct perception.It includes three components: inhibition control,working memory and cognitive flexibility(Diamond,2013).The development of executive function starts from early childhood and runs through adolescence until adulthood.For children in the pre-adolescence(6-12 years old),this age is not only the stage with the greatest change in executive function,but also their cognitive development and academic achievements are related to executive function.Therefore,what factors will affect the executive function of children in preadolescence is a problem that researchers are concerned about.Exercise has many positive effects on people's physiology and psychology,so it is often used as an intervention to improve cognitive functions.Some researchers have suggested that executive function is the most sensitive cognitive component of exercise.In order to explore the relationship between exercise and children's executive function,previous researchers used randomized controlled experimental design to investigate the effect of exercise intervention on children's executive function.Most studies have found that regardless of whether the investigator used short-term exercise or longterm exercise intervention methods,children's executive function has significantly improved after intervention(short-term exercise: Chen,Yan,Yin,Pan & Chang,2014;long-term exercise: Alesi,Bianco,Luppina,Palma & Pepi,2016).However,there are two general problems with this type of intervention research: first,exercise intervention does not bring about a general improvement in the various components of children's executive function.De Greeff et al.(2017)found through metaanalysis that short-term exercise intervention can significantly improve children's inhibition control,and long-term exercise intervention can significantly improve children's working memory and cognitive flexibility;second,the ecological validity of intervention research is low,and it is difficult to promote the result in society.Therefore,another direction deserves the attention of researchers: encourage children to use more time in daily life,after school,and sports class to develop a "active" lifestyle.In order to achieve this goal,the researchers explored the relationship between children's exercise level in daily life and executive function through cross-sectional experimental design.Although some studies have found that children's exercise levels in daily life are positively correlated with executive function(e.g.,Ishihara,Sugasawa,Matsuda and Mizuno,2017),some studies have also found inconsistent results(e.g.,Niet,Smith,Scherder,Oosterlaan & Visscher,2014).Therefore,more research is still needed to reveal the relationship between children's exercise level in daily life and executive function.At the same time,some researchers began to pay attention to the underlying neural mechanism behind exercise and executive function.Researchers generally believe that exercise changes children's brain activation patterns or brain structure,thereby enhancing executive function.Some studies have found that in children who received exercise intervention or have stronger exercise ability,the frontal lobe,parietal lobe and dorsal striatum area activation reduced during the related tasks of inhibition control(e.g.: Chaddock-Heyman et al.,2013;Chaddock et al.,2012a;Chaddock et al.,2012b).This activation mode may be related to a more effective cognitive strategy,that is,it requires less cognitive resources to complete the task.Studies have also found that the hippocampus plays a key role in exercise levels and children's working memory(Chaddock et al.,2010a;Chen,Zhu,Yan & Yin,2016).Although previous researches on task-state fMRI have revealed the neural mechanisms of some children's exercise on executive function,these studies have two deficiencies.First,few studies have explored the underlying neural mechanisms of children's motor and executive functions from the perspective of resting-state fMRI.Krafft et al.(2014a)found that exercise intervention can change children's default network,cognitive control network,and motor network motivation during restingstate,but the researchers did not connect this change with executive function;second,in the past neuroimaging studies,few researchers explored exercise,brain activation and executive function through mediation analysis.Only Chaddock et al.(2010a)found that the volume of bilateral hippocampus mediates the relationship between fitness and children's working memory.Therefore,more research is needed to reveal the potential neural mechanism of children's movement and executive function through the resting-state fMRI and the establishment of mediation model.Based on previous research,this study aims to explore the relationship between children's daily exercise level and executive function,and further explore its potential neural mechanisms through the perspective of resting-state fMRI and mediation analysis.Study 1 used children from 9-12 years old in two elementary schools as subjects(N=130).The children's exercise level in daily life was measured using the International Physical Activity Questionnaire for children.Emotional Simon task,Wechsler Child Intelligence Scale and Wisconsin Card Sorting Task were used to measured children's inhibition control,working memory,and cognitive flexibility.It was found that children with higher levels of exercise performed significant better in working memory tasks,while not significant in tasks that inhibited control and cognitive flexibility.Studies 2 and 3 used resting-state fMRI to measure the brain activity of the same group of children.In study 2,Regional Homogeneity,Amplitude of Low Frequency Fluctuations,and fraction Amplitude of Low Frequency Fluctuations were used as the dependent variables to reflect the resting brain activities.The correlation between children's exercise and these three indicators was explored through correlation analysis.It was found that there was a significant positive correlation between the children's exercise level and the two important components of the parietal memory network,the fALFF signal of the precuneus and the mid-cingulate gyrus,while the exercise level was not related to the Reho and ALFF signals of the whole brain.In study 3,four regions of the parietal memory network were selected as regions of interest,and the resting-state functional connectivity(rsFC)map of each region of interest was calculated as the dependent variable.It was found that when the left posterior parietal lobe was used as the region of interest,the level of exercise was positive related to the rsFC of left posterior parietal lobe and right inferior temporal gyrus,bilateral medial frontal gyrus,bilateral posterior cingulate gyrus,right angular,the dorsallateral prefrontal lobe and the superior frontal gyrus.In study 4,based on the first three studies,we chose children's exercise level as the independent variable,resting-state brain activity as the mediator,and performance of the behavioral tasks as the dependent variable.The results showed that the functional connection between left inferior parietal lobule and bilateral medial frontal gyrus partially mediated the positive correlation between exercise level and working memory task performance.In summary,the results of this study provide evidence that although compared with exercise interventions,children's exercise in daily life is less intense than exercise intervention,but children's exercise level in daily life is still It is related to the executive function,and is only related to some components of the executive function,not all the components.In addition,according to the results of this study,the level of exercise in daily life may have a direct impact on children's working memory ability,while indirectly affecting children's working memory ability by changing the way children's resting brain activities.This study is the first to use resting state MRI and intermediary analysis methods to explore the relationship between children's daily exercise level and executive function.Based on previous research,this study theoretically provides new evidence for exploring the relationship between children's movement and executive function and potential neural mechanisms;in application,it helps encourage children to use their spare time to leave their seats and exercise more,It also provides a possible practical direction for how to effectively use exercise to improve children's cognitive abilities.