| Smoking,known as tobacco dependence,is highly addictive.It has been defined by the World Health Organization as a psychiatric disorder.As one of the most severe problem of public health worldwide,smoking addiction is thought to be a significant cause of cardiovascular diseases,lung diseases,and preventable death.However,the phenomenon that the age of people who smoke tends to be lower is more concerning.In china,the rate of young smokers increased year by year,so it is necessary to understand the smoking status and variation trend timely and accurately.Adolescence and young adulthood is a very important stage which is encompassed by alterations in physical,psychological,and social function.During this special period,their brains are still in continuous development and have high neural plasticity.They are lack of cognitive control and inhibitory processing,which makes them vulnerable to drug abuse during this period.In another aspect,smoking during adolescence and young adulthood may produce neurophysiological and cognitive control changes that may promote nicotine dependence later in life.Thus,it is extremely important to study the relationship between smoking and anatomical brain structural and functional alterations in this age group,which can provide effective theoretical support for its intervention and treatment.At present,some scholars,at home or abroad,use various imaging techniques to study the brain structure and function of smokers,making us have a preliminary understanding of smoking addiction.However,academic circles still lack the unified conclusion of the deep mechanism of smoking addiction,and especially we don't have a clear understanding of the neural physiological characteristics of adolescent smoking.For the core issue of smoking addiction that cause relapsing,namely persistent desire and the reduction of cognitive control ability in the abstinence state,the researches are not enough.Therefore,based on the former investigations,this paper studied the brain abnormalities of young smokers by using magnetic resonance imaging(MRI).The main research results obtained and the innovation points are as follows:Firstly,as voxel-based morphometry(VBM)has certain limitations,and the measurement results show inconsistency sometimes,we used cortical thickness measurement to examine the structure differences of the brain cortex between young adult smokers and their age-matched,non-smoking peers,which is more precise than VBM.In conclusion,our study showed regional cortical thickness reductions in young male adult smokers compared to matched nonsmokers.In addition,we also found that brain structural changes in the DLPFC and OFC were associated with the degree of nicotine dependence and the cumulative amount of nicotine intake respectively.We suggest that the structural abnormalities of the brain regions associated with cognitive control(especially the frontal region)may indicate that young smokers appeared abnormal self-control function,which makes it hard for smokers to effectively control smoking behavior.The striatum plays important role in addiction.However,previous research did not find smokers have structural abnormalities in this brain region.As a supplement of cortical thickness study in young smokers,in the second study,we used subcortical volume measurement to examine the morphological differences of the striatum between young adult smokers and nonsmokers.We found increases in the volumes of striatal regions in young male adult smokers compared to nonsmokers.Combined with the first research conclusion,our findings showed structural abnormalities of the key nodes in the fronto-striatal circuits in young male adult smokers.These brain deficits(reduced frontal cortical thickness and increased striatal volume)may suggest an imbalance between cognitive control(reduced protection factors)and reward drive behaviours(increased risk factors)associated with smoking addiction and relapse.On the network level,the salience network(SN)is associated with hierarchical initiation of cognitive control signals and plays an important role in identifying relevant internal and external stimuli in order to guide behavior,which is critical for the development of nicotine dependence.In the current study,we used multimodal neuroimaging methods(diffusion tensor imaging and resting-state functional connectivity)to analyze the brain structural and functional characteristics within SN between young smokers and nonsmokers.We found abnormal RSFC and structural integrity(FA)between the ACC and insula within the SN in young adult smokers.Additionally,the right insula-ACC RSFC was associated with cognitive control deficits measured by the Stroop color-word task in young adult smokers.These findings may provide more scientific evidence for the critical roles of the SN in cognitive control and can shed new insights into the neural mechanism of smoking addiction.Focused on the mechanism of withdrawal on smoking craving,in our fourth study,we used the regional homogeneity(Re Ho)to assess the brain properties between 12-hour of abstinence condition and satiety condition during the resting state in young smokers by employing a within-subject design.We found young smokers in abstinence state(compared with satiety)had higher Re Ho values in brain regions involved in the fronto-striatal circuits,as well as brain regions involved in the DMN.Moreover,we also found significant positive associations between the Re Ho changes and the changes in craving induced by 12-h abstinence in the ACC and the bilateral caudate.The current findings improve our understanding of the effects of acute smoking abstinence on the spontaneous brain activity and may contribute a new insight into the neural mechanism of craving in smoking addiction.In conclusion,smoking can lead to abnormalities of brain structure and function,as well as the cognitive control deficits.Additionally,our findings of the changes in spontaneous brain function activation pattern caused by the withdraw may further perfect the theory about smoking addiction. |
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