Primary Motor Cortex Processing Mechanism Of Automatic Approach Effect On Cigarette Related Cues In Smokers

As the process of nicotine addiction progresses,smokers show some cognitive bias toward cigarette-related cues,such as attentional bias and automatic tendency to approach.Previous studies have shown that smokers’ tendency to auto-approach is associated with smokers` dependence on cigarette and relapse of smoking withdrawal,but the underlying physiological mechanism of auto-approach effect remains unclear.In addition,the primary motor cortex(M1)plays an important role in automatic behavioral expression,and whether M1 is involved in the processing of this effect needs to be further explored.In this study,the implicit self-referential stimulus response compatibility task(manikin SRC)was selected,and the regulatory mechanism of the automatic approach effect of left M1 on smokers to cigarette-related cues was explored by transcranial magnetic stimulation(TMS).Study 1 adopted the online single-pulse TMS(sp TMS)paradigm and applied single-pulse stimulation to the participant’s M1 to investigate the regulatory mechanism of corticospinal excitability in the automatic approach effect.The results of experiment 1 showed that:(1)smokers tended to approach cigarette-related clues faster than avoiding cigarette-related clues,showing automatic approach bias;conversely,non-smokers showed avoiding tendencies.(2)At 200 ms after the appearance of pictures,the motor evoked potential(MEP)amplitude of approaching the cigarette-related clues in smokers was significantly greater than avoiding cigarette-related cues;the non-smokers showed the opposite result,that is,when they avoided the cigarette-related cues,the corticospinal excitability was significantly higher than approaching cues.There was no significant difference between the two groups when performing avoidance tasks on neutral cues.Study 2(Experiment 2 and Experiment 3ab)adopted the paired-pulse TMS paradigm(pp TMS),which applies two pulses to M1 to detect changes in neural circuits within the cortex during the task.The results of experiment 2 showed that the Short Intracortical Inhibition(SICI)of smokers in resting state were significantly higher than those in the control group,while there was no significant difference in Intracortical Facilitation(ICF).Experiment 3ab brought the most sensitive time points of experiment 2,that is,3ms and 12 ms,into the same paradigm as experiment 1,and measured the circuit changes in the task state.The results showed that(1)the ICF circuit in M1 was significantly activated early when smokers approaching cigarette-related cues.(2)The inhibitory circuit(SICI)within M1 is significantly strengthened in the early stages of smokers’ avoidance of cigarette cues.Inhibitory circuits(SICI)in non-smokers are significantly strengthened as they approach cigarette-related cues.From the above research results,the following conclusions can be drawn:(1)The corticospinal cord excitatory amplitude of left M1 can be used as a physiological marker for smokers’ tendency to automatically approach cigaretterelated cues,and this high degree of activation may lead to rapid mobilization of expression of smoking-related behaviors.(2)The intracortical facilitation pathway(ICF)in M1 is involved in the regulation of the auto-approach effect of cigarette-related clues in smokers,and may further accelerate the behavioral response of smokers to automatically approach cigarette clues by promoting corticalspinal excitability.The inhibitory circuit(SICI)in M1 confirms the auto-approach effect of smokers on cigarette-related cues.