| Humans tend to show automatic action(approaching or avoiding)tendency to an external emotional stimulus,which may lead to effective action in a given context,enabling the individuals to make faster decisions and play a crucial role in human behavior.Previous studies have shown that the behavior conducted in a compatible manner(approaching positive stimulus and avoiding negative stimulus)is faster than those conducted in an incompatible manner(approaching negative stimulus and avoiding positive stimulus),which is termed the compatibility effect of approaching the positive and avoiding the negative.However,these studies did not address the underlying neurophysiological mechanisms of the emotional compatibility effect to explain why the reaction times are faster for compatible compared to incompatible behavior.In addition,the dorsolateral prefrontal cortex(DLPFC),as an entry node in the brain for cognitive and executive processes,is involved in this effect,with a controversial regulating mechanism.The manikin task has been taken as the paradigm for investigating the emotional approaching-avoiding behavior,with the transcranial magnetic stimulation(TMS)used as the tool to demonstrate the physiological mechanism,as well as the regulating mechanism of DLPFC on the emotional approaching-avoiding behavior.In the Study1,the online single pulse TMS or paired-pulse TMS was applied on either the left or right M1 to investigate the corticospinal excitability and intracortical inhibition and facilitation of primary motor cortex(M1)during the manikin task,to further reveal the physiological mechanism of the emotional compatibility effect.Exp 1 results showed that:(1)the reaction of the compatible behavior was faster than incompatible behavior;(2)at the 150 ms and 200 ms after the emotional stimulus onset,motor evoked potentials(MEPs)of left M1 was significantly higher in the compatible behavior than in the incompatible behavior;(3)at the 150 ms after the emotional stimulus onset,MEPs of right M1 was significantly higher in the incompatible behavior than in the compatible behavior.Exp 2 results showed that:(4)compared with the incompatible behavior,the compatible behavior shown a significant intracortical facilitation.In the Study 2,theta burst stimulation(TBS),one paradigm of repetitive transcranial magnetic stimulation(r TMS),was used: excitatory intermittent TBS(i TBS)and inhibitory continuous TBS(c TBS)or sham was applied either left or right DLPFC and the change of the behavior performance was used to assess the causal relationship between the DLPFC and the emotional approaching-avoiding behavior.Exp 3 results showed that:(1)the excitatory i TBS applied over the left DLPFC accelerated the compatible behavior,whereas inhibitory c TBS applied over the left DLPFC accelerated the incompatible behavior;(2)the excitatory i TBS applied over the right DLPFC accelerated the avoiding behavior,whereas inhibitory c TBS applied over the right DLPFC accelerated the approaching behavior.In the Study 3,dual-site TMS was used to investigate the connectivity of the left DLPFC-M1 and right DLPFC-M1 during the manikin task,with the first stimulation applied on the left or right DLPFC and the second one applied on the left M1,to reveal the regulating mechanism of the DLPFC on the behavior.Exp 4 results showed that:the left DLPFC-M1 connectivity was facilitated in the incompatible behavior in the ISI at 25 ms;Exp 5 results showed that: right DLPFC-M1 connectivity didn’t change in approaching-avoiding behavior.Hence,it could be concluded that:(1)the MEPs from the bilateral M1 in this early processing stage could be a physiological marker of the generation of emotional compatibility effect,and compatible behaviors conducive to individual survival and development will lead to a high degree of activation of the motor system;(2)left DLPFC could be a key node to modulate emotional compatibility effect in the human brain;(3)left DLPFC facilitates the incompatible behaviors. |
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