11
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      What can mirror-touch synaesthesia tell us about the sense of agency?

      editorial

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Sense of agency (SoAg) refers to the feeling of control over one's actions and forms an integral part of our cognitive and social lives (Moore and Fletcher, 2012). For example, it is thought that the recognition of oneself as the agent of an action plays a fundamental role in self-awareness (Jeannerod, 2003). It is also thought that the experience of agency is important for guiding our attributions of responsibility (Haggard and Tsakiris, 2009). The importance of SoAg is also demonstrated by the striking changes in this experience associated with various psychiatric (e.g., schizophrenia) and neurological (e.g., cortico-basal degeneration) disorders. While in recent years a number of studies have examined SoAg in these clinical groups, one group of individuals that have not yet been examined are those with mirror-touch synaesthesia (MTS). This opinion article seeks to explain why changes in SoAg may occur in MTS and also why mirror-touch synaesthetes could offer unique insights into the neurocognitive basis of SoAg. For most of us, observing another person being touched activates neural regions in the somatosensory cortex that are also involved in experiencing touch (e.g., Keysers et al., 2004, 2010; Ebisch et al., 2008; Schaefer et al., 2012), however this activation does not lead to overt sensations of the observed event: we typically do not feel any tactile sensation when observing the tactile experience of others. On the contrary, people with MTS, approximately 1.6% of the population (Banissy et al., 2009), do experience overt tactile sensations to the observed event: they feel tactile sensations on their body when simply seeing touch to another's body (Blakemore et al., 2005; Holle et al., 2011; Banissy, 2013). These experiences are reported to be automatic (Banissy and Ward, 2007), enduring (Holle et al., 2011), and may be associated with broader differences in social perception (Banissy and Ward, 2007; Banissy et al., 2011; Goller et al., 2013). Recent studies (e.g., Aimola-Davies and White, 2013; Holle et al., 2013; Maister et al., 2013) suggest that individuals with MTS have atypical self-other representations. For example, Maister et al. (2013) ran a study using the “enfacement illusion” paradigm. In the typical “enfacement illusion,” participants are asked to say to what extent images of faces that were morphed between themselves or another person look like themselves or the other; they then watch a video in which the other person is touched in synchrony and congruent with a felt touch on the participant's face. After experiencing a synchrony between the observed and felt touch, the images that participants had initially perceived as containing equal quantities of self and other became more likely to be recognized as the self (Tsakiris, 2008; Tajadura-Jiménez et al., 2012). Maister et al. (2013) adapted this paradigm in MTS, by removing the physical touch component. That is to say that individuals observed touch to other people, but veridical synchronous touch was not physically applied to the face. They showed that MT synaesthetes experienced the same effect of “enfacement illusion” in the absence of a touch applied to their face, concluding that simply viewing the touch on others evokes changes in self-other representations in MTS. In this regard, MTS may therefore be characterized as bringing more malleable body representations, reflecting a blurring in the self-other distinction processes (Banissy and Ward, 2013; Maister et al., 2013). This self-other blurring may be significant for SoAg. Experimental work in neurotypical individuals has shown how the deliberate blurring of the boundaries between self and other can have dramatic effects on SoAg. A good example of this is the so-called “Vicarious Agency” illusion, first demonstrated by Wegner et al. (2004). In this paradigm, participants sit in front of a mirror with their arms placed out of view, under a sheet that covers everything below their shoulders. A cardboard shield is placed behind their back to block their view of the experimenter standing behind them. The experimenter places their arm forward so that it appears where the participant's own arm would have been. This set-up is therefore aimed at engendering self-other confusion. Participants are then asked to look at the mirror in front of them, while the experimenter performs the gestures. Participants also wear headphones on which are played action previews (e.g., “wave your hand,” “make the ok gesture”). These previews are either congruent or incongruent with the actions subsequently made by the experimenter. Wegner et al. found that participants experienced a SoAg and ownership over the arm that appeared in the mirror and that their experience of controlling the movements was increased when the previews were congruent with the action the experimenter made. In this way, we can see how an experimentally-induced blurring of the boundaries between self and other has a striking effect on SoAg. A strong prediction from this finding is that individuals with MTS will be more vulnerable to these agency illusions. This is something we are currently testing. Another line of enquiry worth pursuing is whether or not these putative agency effects in MTS are mediated by the changes in the sense of body ownership associated with the condition (e.g., Aimola-Davies and White, 2013; Maister et al., 2013). The sense of body ownership refers to the feeling that the body one inhabits is one's own. Importantly, the sense of body ownership and SoAg are not independent. For example, it is often assumed that SoAg is predicated on recognizing that the moving body part is one's own. The existing work on MTS would suggest that changes in sense of ownership represent a primary disturbance in the condition. One prediction, therefore, is that the putative changes in SoAg are a consequence of these fundamental disturbances in sense of ownership. Intriguingly, the relationship between agency and ownership can also work in the opposite direction. Previous research in neurotypical adults has shown that SoAg can play a role in structuring bodily awareness (e.g., Tsakiris et al., 2010). In the context of MTS, one prediction from this would be that if there were agency-processing deficits these would exacerbate more basic disturbances in bodily awareness. We are clearly suggesting here that MTS is primarily a “disorder” of ownership, which can have consequences for SoAg and which in turn can further worsen ownership disturbances. However, at present this is speculative and is something that should be systematically examined in future research. A further benefit of examining of SoAg in MTS is that it may help constrain our understanding of how inter-individual differences in self-other representations involved in SoAg and sense of body ownership interact to structure bodily awareness. Indeed, it has been shown that patients with impairments in self-other discrimination perform poorly on agency tasks: in particular, Daprati et al. (1997) showed that people with schizophrenia had difficulties when required to correctly identify the origin of an action. Even in the absence of clinical implications, it is likely that individuals with MTS can experience a distortion in their SoAg and could be a non-clinical framework for studying the determinants of agency and its disruptions. It is in this context that MTS may also help inform models of SoAg, increasing our understanding of the interaction between ownership and agency. It is our contention that MTS offers a rare opportunity to investigate this interaction more directly. In the context of existing models of SoAg there are also some specific predictions about agency processing in MTS that could be tested. For example, the so-called comparator model of SoAg (e.g., Blakemore et al., 2002) states that predicted sensory feedback is subtracted out of the actual sensory percept during movement. According to the model this sensory attenuation is a key mechanism that allows us to distinguish between self- and externally-generated effects. Previous work in neurotypical individuals has shown that sensory suppression is only found for self-generated movements and not when observing someone else move (Weiss and Schütz-Bosbach, 2012). However, given the disturbances in self-other discrimination in MTS one might predict that individuals with MTS would also show sensory suppression effects when observing someone else move. The final benefit of research on MTS that we wish to highlight concerns the brain basis of SoAg. Although a great deal of work has been done on the neural correlates of SoAg, we still know relatively little about the neural networks and mechanisms underpinning it (see David, 2012, for a review). We would suggest that research on MTS could help in this regard by furnishing our understanding of the brain basis of SoAg. Two regions commonly implicated in SoAg are the anterior insula and temporo-parietal junction (TPJ). The anterior insula is heavily linked with self-other discrimination (Ruby and Decety, 2001) and is also activated in agency attribution tasks (e.g., Farrer and Frith, 2002). Concerning the TPJ, many studies on SoAg that rely on the comparison between self-generated and the externally produced sensory signals have found activation in the right TPJ (Ruby and Decety, 2001; Farrer et al., 2003; see Decety and Lamm, 2007 for a meta-analysis of fMRI studies on TPJ). Interestingly, the anterior insula and TPJ also appear to play a key role in MTS. A common suggestion is that MTS reflects a hyper-activation of the mirror-touch network; that is, brain regions involved in experiencing and passively observing touch to others, including the primary and secondary somatosensory cortices (SI, SII) (Blakemore et al., 2005; Holle et al., 2013). Banissy and Ward (2013), suggest that this hyper-activation of the mirror-touch system in individuals with MTS may be gated by atypical functioning in neural regions involved in self-other representations, and highlight potential roles for both the anterior insula and the TPJ in this process. One potential avenue for future research would be to examine whether this putative gating mechanism is functionally relevant for SoAg, perhaps having a role in modulating more basic sensorimotor processes known to be important for this experience. In summary, MTS refers to a rare experience in which observing touch or pain to another person evokes a tactile experience on the observer's body. There is growing evidence to suggest that this is linked to a blurring of self-other representation. In this article we have discussed how this disturbance may produce changes in SoAg in MTS. We have also discussed the ways in which research on MTS can improve our understanding of the neurocognitive basis of SoAg. In light of these discussions we believe that future research on SoAg in MTS is likely to provide valuable insights, both for those with a primary interest in MTS and for those with a primary interest in SoAg. Conflict of interest statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

          Related collections

          Most cited references18

          • Record: found
          • Abstract: found
          • Article: not found

          The role of the right temporoparietal junction in social interaction: how low-level computational processes contribute to meta-cognition.

          Accumulating evidence from cognitive neuroscience indicates that the right inferior parietal cortex, at the junction with the posterior temporal cortex, plays a critical role in various aspects of social cognition such as theory of mind and empathy. With a quantitative meta-analysis of 70 functional neuroimaging studies, the authors demonstrate that this area is also engaged in lower-level (bottom-up) computational processes associated with the sense of agency and reorienting attention to salient stimuli. It is argued that this domain-general computational mechanism is crucial for higher level social cognitive processing.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Effect of subjective perspective taking during simulation of action: a PET investigation of agency.

            Perspective taking is an essential component in the mechanisms that account for intersubjectivity and agency. Mental simulation of action can be used as a natural protocol to explore the cognitive and neural processing involved in agency. Here we took PET measurements while subjects simulated actions with either a first-person or a third-person perspective. Both conditions were associated with common activation in the SMA, the precentral gyrus, the precuneus and the MT/V5 complex. When compared to the first-person perspective, the third-person perspective recruited right inferior parietal, precuneus, posterior cingulate and frontopolar cortex. The opposite contrast revealed activation in left inferior parietal and somatosensory cortex. We suggest that the right inferior parietal, precuneus and somatosensory cortex are specifically involved in distinguishing self-produced actions from those generated by others.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Modulating the experience of agency: a positron emission tomography study.

              This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.
                Bookmark

                Author and article information

                Contributors
                Journal
                Front Hum Neurosci
                Front Hum Neurosci
                Front. Hum. Neurosci.
                Frontiers in Human Neuroscience
                Frontiers Media S.A.
                1662-5161
                24 April 2014
                2014
                : 8
                : 256
                Affiliations
                Department of Psychology, Goldsmiths, University of London London, UK
                Author notes

                This article was submitted to the journal Frontiers in Human Neuroscience.

                Edited by: Nicole David, University Medical Center Hamburg-Eppendorf, Germany

                Reviewed by: Bigna Lenggenhager, University Hospital Zurich, Switzerland

                Article
                10.3389/fnhum.2014.00256
                4006043
                24795610
                cd9f6a24-7532-486b-9aaa-0dd15187e3c4
                Copyright © 2014 Cioffi, Moore and Banissy.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 18 March 2014
                : 07 April 2014
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 30, Pages: 3, Words: 2703
                Categories
                Neuroscience
                Opinion Article

                Neurosciences
                agency,mirror-touch synaesthesia,self-other distinction,ownership,self-other representation

                Comments

                Comment on this article

                scite_
                36
                0
                10
                0
                Smart Citations
                36
                0
                10
                0
                Citing PublicationsSupportingMentioningContrasting
                View Citations

                See how this article has been cited at scite.ai

                scite shows how a scientific paper has been cited by providing the context of the citation, a classification describing whether it supports, mentions, or contrasts the cited claim, and a label indicating in which section the citation was made.

                Similar content1

                Cited by4

                Most referenced authors134