Editorial: What can we make of theories of embodiment and the role of the human mirror neuron system?

摘要

Over the last 20 years, work surrounding theories of embodiment and the role of the putative mirror neuron system (MNS) in humans has been hotly debated. In 2000, Ramachandran ( 2000 , p. 1) suggested that mirror neurons would do for psychology what DNA did for biology, providing “a unifying framework” that would help explain a host of mental abilities.” In fact, the strong evidence for action/perception coupling observed in macaque mirror neurons led several authors to implicate this system in higher order functions in humans, such as empathy, language and theory of mind (Rizzolatti and Arbib, 1998 ; Gallese et al., 2004 ; but see Hickok, 2009 ). Thus, embodiment is a broad area of study that suggests that motor resonance participates in several of these higher order processes. However, the exact role played by specific brain structures and/or actual mirror neurons in these processes varies greatly across theories and authors. This special issue brought together 12 studies conducted with healthy as well as brain-injured populations, behavioral as well as imaging techniques (functional and structural), and opinion pieces and responses. Through this broad landscape, we offer a fresh and frugal approach to the challenges and controversies of the translational neuroscience of embodiment and the MNS. Two of the articles in this collection addressed how the human MNS might underlie the physiological mechanisms that give rise to human emotions. In “Motor empathy is a consequence of misattribution of sensory information in observers,” Mahayana et al. ( 2014 ) used TMS to measure participants' reactions while they observed videos of painful stimuli being inflicted on another person. Their results suggest that empathy may be partially caused by a misattribution of perceptual information: pain experienced in someone else is perceived as occurring in oneself. This finding raises an interesting and novel view on embodiment that suggests that the empathy experienced through our mirror system is in fact selfish, as it mostly reflects empathy toward ourselves. In “Washing the guilt away: effects of personal versus vicarious cleansing on guilty feelings and prosociality,” Xu et al. ( 2014 ) asked participants to write about a guilt-inducing past wrong and were then asked to wash their hands, watch a video of someone washing their hands, or a video of someone typing. They were then asked whether they would help a Ph.D. student with her thesis by answering some questions. Participants who felt the least guilty were those who washed their hands, followed by those who watched the hands-washing video, and then by those who watched the typing video. Also, participants who felt most guilty were more likely to help the student with her project. The authors conclude that washing one's hands or watching someone else washing their hands can be good for feelings of guilt, but not compassion. Both studies offer new evidence for the connection between inner ‘motor resonance’ and emotion (i.e., Wicker et al., 2003 ). Also, the study by Xu et al. and that of Kacinik (see below) are classic examples of embodied language, where even the enactment of metaphorical expressions can strongly activate the mirror neuron system. In “Language comprehension warps the mirror neuron system,” Zarr et al. ( 2013 ) asked participants to read sentences describing the transfer of objects away or toward the reader. The adapting sentences disrupted prediction of actions in the same direction, but (a) only for videos of biological motion, and (b) only when the effector implied by the language (e.g., the hand) matched the videos. Similarly, Kacinik ( 2014 ) asked participants to read a story and act out the idioms presented (e.g., literally sitting on the fence, on the edge of one's seat) in “Sticking your neck out and burying the hatchet: what idioms reveal about embodied simulation.” They found that the process of embodying idioms simply by engaging in the corresponding actions activated their meaning enough to significantly influence subsequent processing and judgments. Finally, in “Action relevance in linguistic context drives word-induced motor activity,” Aravena et al. ( 2014 ) analyzed online modulations of grip force while subjects listened to target words embedded in different linguistic contexts. They conclude that motor structure activation is part of a dynamic process that integrates the lexical meaning potential of a term and the context in the online construction of a situation model, which is a crucial process for fluent and efficient online language comprehension. Similarly to Xu et al. (see above), these three articles support the notion that the motor resonance of language strongly influences its comprehension. The strict version of this view, which argues that semiotic coding would mostly rely on the human MNS (see Pulvermüller et al., 2014 ), continues to be controversial and is challenged by other articles in this topic (see below). Two ar