| Background and PurposeNicotine can lead to homeostasis and neuroadaptation.Long term exposure can lead to dependence.The typical characteristics are compulsive smoking behavior and withdrawal symptoms.Because of its easy availability,tobacco control is very urgent.Understanding the neural mechanism of tobacco addiction is helpful to guide smoking cessation scientifically.Functional magnetic resonance imaging(fMRI),a technology in brain science,is unique in brain function assessment with its advantages.Functional connectivity density is a method to explore voxel centrality through functional connectivity sparsity,which has the advantage of analyzing the whole brain at one time.This study takes the time fluctuation of neural activity into account,and uses the dynamic functional connectivity density(dFCD)to analyze the dynamic changes of brain functional network at the whole brain and hemisphere level,which is helpful to better explore the essence of brain functional changes in nicotine dependent patients.Materials and MethodsIn this study,70 Han male nicotine addicts and 40 healthy controls were included in the study.The brain functional magnetic resonance images of all the subjects were collected.The dynamic functional connectivity density of the whole brain and hemisphere was calculated based on the functional data.First,the two groups were compared,and then the smokers were divided into mild dependence group(37 cases)and severe dependence group(33 cases)according to the degree of dependence.Then,ANOVA was used for comparison among the three groups,and along with pairwise comparison between the two groups.The mask of difference region in the results of ANOVA was used as the template in the two sample t test.All the results were corrected by GRF.The significance levels of voxel and cluster were P<0.001 and P<0.05 respectively.Then the results are verified by changing the width of the sliding window.Finally,the region of interest(ROI)with a radius of 5 mm was delineated by taking the extremum of brain regions with significant difference between the nicotine dependent group and the control group as the center of the ball,and the average value of ROIs’ dynamic functional connectivity density was extracted and correlated with smoking related clinical parameters.Results1.The dynamic characteristics of functional integration between nicotine dependent and control groups were compared:(1)Whole-brain level:There was no significant difference;(2)Hemispheric level:A.Compared with the control group,the dFCD of the gray matter in the temporal lobe,parietal lobe,frontal lobe,and insula increased both within and between hemispheres in smokers,and the intra-and interhemispheric dFCD of occipital gray matter decreased;B.Smokers also showed an increase in intrahemispheric dFCD in the local gray matter of inferior frontal gyrus and parietal lobe,and a decrease in intrahemispheric dFCD in the gray matter of temporal lobe,frontal lobe,parietal lobe,and marginal lobe.2.The dynamic characteristics of functional integration among the groups with different nicotine dependence were compared:(1)Whole-brain level:There was no significant difference;(2)Hemispheric level:A.Compared with the control group,the dFCD of local gray matter in the occipital lobe,temporal lobe,and parietal lobe increased both within and between hemispheres in the severe dependence group,the dFCD of local gray matter in the frontal lobe,insular lobe,temporal lobe,and occipital lobe decreased both within and between hemispheres;The interhemispheric dFCD in the superior frontal gyrus/middle cingulate gyrus decreased in the severe dependence group;B.Compared with the control group,the intra-and interhemispheric dFCD of the occipital cortex decreased in the mild dependence group;C.Compared with the mild dependence group,the intra-and interhemispheric dFCD of the occipital cortex,temporal cortex increased in the severe dependence group;Besides,compared with the mild dependence group,the interhemispheric dFCD in the cingulate gyrus/limbic lobe hemispheres of the severe dependence group decreased,while the intrahemispheric dFCD in the parietal cortex increased.3.Correlation analysis:(1)a.The results showed that the ROI’s dFCD of the left temporal lobe was negatively correlated with FTND values(r=-0.260,P=0.030),positively correlated with the age of initial smoking(r=0.276,P=0.021),and no significant correlation with daily smoking volume,pack-year,and smoking age;b.There was a negative correlation between the ROI’s dFCD of the left Calcarine fissure and surrounding cortex and FTND(r=-0.255,P=0.033),but no significant correlation with daily smoking,pack-year,smoking age and initial smoking age;c.No correlation was found between dFCD and smoking-related clinical indicators in other ROIs.(2)The FTND values were positively correlated with pack-year(r=0.445,P=0.000),daily smoking(r=0.371,P=0.002)and smoking age(r=0.285,P=0.017);And pack-year and smoking age were negatively correlated with education level,the related indicators were(r=-0.417,P=0.000)and(r=-0.465,P=0.000)respectively.4.Verification analysis:The dynamic characteristics of functional connectivity density in the brain cortexes were obtained by changing the length of the sliding window.The results showed that the dynamic characteristics of functional connectivity density at the whole-brain and hemisphere level between the nicotine dependent and the control were different slightly in different window widths,but the differences between the groups were stable.ConclusionsThere is the phenomenon of visual network separation at the cerebral hemispheric level in Nicotine-dependent crowds,which may be related to the impairment of executive cognitive function related to arbitrary visuomotor.At the cerebral hemispheric level,the altered dynamic functional connection density of brain regions related to cognitive,executive control,emotion,attention,and behavior may be the compensation for the impairment of brain function in the heavy nicotine-dependent crowds. |
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