The Role of the Right Temporoparietal Junction in the Control of Imitation

Cerebral Cortex April 2015;25:1107–1113 doi:10.1093/cercor/bht306 Advance Access publication October 31, 2013 The Role of the Right Temporoparietal Junction in the Control of Imitation Sophie Sowden and Caroline Catmur Department of Psychology, University of Surrey, Guildford GU2 7XH, UK Address correspondence to Caroline Catmur. Email: Keywords: imitative compatibility, self–other control, social cognition, TPJ, transcranial magnetic stimulation Introduction A fundamental aspect of social cognition is the ability to distinguish, and switch between, representations of the self and other people. For example, when taking another person’s perspective, switching between “self” and “other” representations is required in order to inhibit the representation of one’s own perspective and to enhance the representation of the other’s perspective. Similarly, in theory-of-mind tasks, one needs to represent the beliefs, desires, or intentions of another person, rather than one’s own beliefs, desires, and intentions. When empathizing with another person, the affective state that results from representation of the other’s emotions must be distinguished from one’s own (Singer and Lamm 2009), again requiring the ability to switch between representations of one’s own and others’ emotions. Finally, the control of imitation, a key aspect of social interaction (Chartrand and Bargh 1999), requires one to switch between motor representations activated by the observation of another’s actions and self-generated motor representations (Brass et al. 2009). Although these tasks involve different higher-level social cognitive processes, there is some evidence that a common lower-level process may contribute to all of them (Decety and Lamm 2007). This lower-level process may be the ability to control, or more specifically switch between, representations of the self and the other, whether these be representations of visual perspectives, mental states, emotions, or actions. In this framework, the requirement for the control of self and other representations occurs whenever the task requires the participant to excite one representation, while inhibiting the other. In this paper, we use the term “switching between” the 2 representations to refer to this process of exciting the selfrepresentation and inhibiting the other-representation, or vice versa. In the case of theory-of-mind tasks, the 2 representations are of the mental states of the self and other, for example, in Young, Camprodon, et al.’s (2010) moral judgment task: I know the powder is sugar; but Grace believes it is toxic. I need to inhibit the representation of my mental state and to excite that of Grace’s in order to carry out the task (in this example, the task requires me to assess her morality when putting the sugar labeled “toxic” into her friend’s coffee). In the case of the control of imitation (e.g., Brass et al. 2001), the 2 representations are motor representations, for example: as a result of task instructions, I intend to lift my index finger, and activate the motor representation for index finger lifting; but the sight of someone else lifting their middle finger activates the motor representation for middle finger lifting. I need to inhibit the motor representation of the other person’s action and to excite my self-generated motor representation in order to perform the task successfully. It can, therefore, be argued that the ability to switch between representations of self and other, whether these are mental representations in the case of theory of mind, motor representations in the case of imitation, or representations of visual perspective or emotions, helps to facilitate successful social cognition. The neural basis of this ability to switch between representations of self and other has been investigated by searching for common neural correlates of these social cognitive tasks. A number of meta-analyses have demonstrated the recruitment of the right temporoparietal junction (rTPJ) in perspectivetaking, theory of mind, and empathy (Decety and Sommerville 2003; Decety and Lamm 2007; van Overwalle 2009). The control of imitation has also been investigated extensively by Brass and colleagues (Brass et al. 2005, 2009; Spengler et al. 2009). Using functional magnetic resonance imaging (fMRI), these researchers found an increased response in the rTPJ, as well as in the medial prefrontal cortex, when participants have to control the tendency to imitate the actions of others. However, since the majority of evidence summarized above has come from correlational brain imaging studies, there is relatively little causal evidence for the role of the TPJ in tasks that require switching between self and other representations. Lesion studies which investigate this question using higher-level social cognitive tasks provide mixed support. For example, Samson et al. (2004) demonstrated impaired theory-of-mind ability in 3 patients with left TPJ lesions. On the other hand, Spengler et al. (2010) did not find an overall deficit in the ability to control imitation in a group of patients with lesions to either the left or right © The Author 2013. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals. Controlling neural representations of the self and other people is fundamental to social cognition. Brain imaging studies have implicated the right temporoparietal junction (rTPJ) in this ability, but causal evidence for its role is lacking. A debate is also ongoing regarding whether the control of, or switching between, self and other representations is a specialized or domain-general process: the rTPJ’s well-established role in reorienting attention supports a domaingeneral process, but a role specific to social cognition has also been proposed. Neuronavigated repetitive transcranial magnetic stimulation was used to target the rTPJ (and a control mid-occipital site) during a task requiring participants to switch between representations of others’ actions on both a social and a nonsocial level, by manipulating imitative and spatial compatibility simultaneously and independently. Both imitative and spatial compatibility effects were apparent on response times; however, the effect of imitative compatibility was significantly stronger, indicating less control of imitation, during stimulation of the rTPJ relative to the control site. This suggests that the rTPJ is involved in switching between self and other representations, and further, that this process may not be entirely domain general. 1108 Control of Imitation by rTPJ • Sowden and Catmur conditions are intended to control for domain-general processing, they often involve d (...truncated)