Botulinum toxin type A(BTX-A)induces a reversible muscle paralysis at the injection site.There is evidence that BTX-A injection in specific facial muscles affects emotional experience and the processing of emotional stimuli(e.g.,facial expressions,emotional language,and videos).Neuroscience research showed that BTX-A injection could attenuate amygdala activity,and could affect the neurocognitive function of reward system and other cerebral cortex as well.These findings can be interpreted by facial feedback hypothesis and social feedback hypothesis from the individual and social perspectives respectively.For subjects who received the injection,BTX-A reduces feedback from facial muscles thus impairing emotional experience and processing.According to this hypothesis,proprioceptive signals from facial muscles are conducted to the mesencephalic trigeminal nucleus and locus coeruleus,the latter of which sends direct projections to the thalamus,basal ganglia,and cerebral cortex related to motor,cognition,and emotion.In interpersonal communication,the observer’s emotional experience becomes similar to the subject who has received BTX-A injection through facial mimicry,and the subject’s emotional experience is also affected by the observer in turn.The mirror neuron system plays an important role in the process.Based on the existing researches,this review proposed an integrated model to explain the cognitive and neural mechanisms of how BTX-A injection affects emotional processing,which deepens the neural basis of facial feedback and social feedback for expression recognition and emotion processing.The model illustrates the roles of facial feedback and social feedback respectively as“signal resource”and“amplifier”of emotional processing caused by BTX-A injection,and the relationship between them.Specifically,the changes in muscles induced by facial mimicry causing emotional synchronization in social feedback process is in line with facial feedback process.The interaction of the two emotional processes could also cause multiple overlapping effects,which exist in both individual emotional processes and interpersonal interactions.Future studies should expand the aspects and levels of emotional processing,such as focusing on subliminal emotion processing and emotion regulation;further explore the mechanisms of how BTX-A injection affects emotional processing using neuroimaging technologies;improve the research paradigms to study the causal relationship between facial feedback and emotional processing;explore the mechanisms and application of BTX-A in the treatment of mental illness like depression;compare the effects of BTX-A injection and other invasive facial procedures on emotional processing.Further research will not only improve the understanding of cognitive and neural mechanisms underlying emotion but also have potential implications in mental health and medical cosmetology.

A型肉毒毒素(简称肉毒素)可引起可逆的局部肌肉麻痹,注射于特定面部肌肉可影响个体的情绪体验,还会干扰个体对情绪性材料(面部表情、语言文字和视频)中情绪信息的加工。认知神经科学研究发现,注射肉毒素会影响杏仁核的激活,影响奖赏系统的功能,以及其他大脑皮层的认知神经功能。面部反馈假说和社会反馈假说分别从个体与社会层面对肉毒素的作用加以解释:注射肉毒素使被注射者的肌肉反馈减少,弱化相应情绪的体验和加工;人际交往中,面部模仿使观察者的情绪体验与被注射者趋同,反过来同样影响被注射者的情绪体验。基于已有研究,本文提出面部反馈与社会反馈的整合模型对注射肉毒素影响情绪加工的认知神经机制进行系统阐释。未来研究可拓展相关的研究范式和方法,关注肉毒素注射对不同层面和水平的情绪加工的影响,及其相应的认知神经机制,进一步明确面部反馈与社会反馈的相互作用,并且考察肉毒素用于抑郁症等心理疾病治疗的作用机制。

国家自然科学基金(62276252)资助项目。