The concept of the self has a long history in philosophy and the sciences, and our attempts to characterise it have led theorists to distinguish between many different forms of self. However, one clear distinction that emerges when reviewing the literature on the self is that between the “bodily” self and the “conceptual” self. The bodily self is thought to be the basis of subjective experience and is grounded in the brain’s sensorimotor processing of the internal and external states of the body. In contrast, the conceptual self is formed of a rich network of associative and semantic information and develops through our interactions with others.
In the psychological sciences, James (
2014) distinguished between the two senses of self, the “me self” which is the self experienced as object and can further be divided into material, social and spiritual aspects, and the “I self” or pure Ego, which is more fundamental and comprises the essence of lived subjective experience. In a similar manner, Neisser (
1991) distinguishes between an ecological self which is developmentally primary and more advanced forms of selfhood such as possession of an extended self or a self-concept which require the ability to reflect on one’s experiences over long time periods and to be able to identify one’s self as part of a larger social group, respectively. Finally based on empirical findings, neuroscience researchers like Damasio (
1999) and Edelman (
2004) have distinguished between a continuously present form of self-awareness, based on the integration of diverse sensory and motor processes (which Damasio terms the “core self” and Edelman terms “primary consciousness”) and a higher-level, temporally extended sense of self which plays a key role in social interaction and in our sense of personal identity. While the multifaceted nature of the concept of self means that any attempt at a binary classification will necessarily be crude and neglect some important nuances, for our current purposes we feel that the separation between bodily and conceptual selfhood captures an important conceptual distinction. In what follows, we will separately review current research regarding the theoretical and neural basis of these two forms of selfhood before moving on to discuss how both forms of the self can be linked to processes involved in social cognition.
Bodily Self
Of these two forms of self, the bodily self is the more fundamental in both developmental and experiential terms. The bodily self is considered to arise from the brain’s integration of multiple signals from different sensory modalities into one coherent multimodal percept (De Vignemont,
2014; Hurley,
1998; Legrand,
2006).
This conception of the bodily self as the nexus of action and perception has also been put forward within the cognitive sciences. Neisser’s (
1991) account of the ecological self, which draws heavily on Gibson’s (
1979) theory of the importance of motor affordances in perception, views the ecological self as being specified largely by objective information which allows for the perception of both the location of the body and how it is interacting with the environment. Neisser considers this information to be largely dependent on knowledge of the body’s movements and their relationship to vision. In addition to Neisser’s focus on the interaction of action and perception, other researchers have emphasised the importance of internal bodily signals (or “interoception”) in generating self-relevant bodily information (Craig,
2003; Damasio,
1999; Seth, Suzuki, & Critchley,
2011). These interoceptive senses include: proprioception or the movements of the musculoskeletal system (Fridland,
2011); the detection of the orientation of the body in space through the vestibular system (Pfeiffer et al.,
2013); the neural and chemical signals indicating the state of one’s cardiac, respiratory and digestive systems (Craig,
2003); and sensory signals for pain, itch, temperature and pleasant touch on the skin (McGlone & Reilly,
2010). The sense of the bodily self is thought to arise when these sensory signals from within the body are then integrated with information from the external senses, primarily vision, to create a multisensory representation of the current state of the body (Seth et al.,
2011).
For much of the history of cognitive science, there was no known methodology that allowed for the manipulation of people’s experience of the bodily self. Although it was known that some neurological conditions could lead to somatoparaphrenia, the loss of a feeling of ownership over one’s limbs (see Vallar & Ronchi,
2009 for a review) examining this sense of body ownership in healthy participants seemed impossible due the difficulty in separating participants from what William James memorably described as “the feeling of the same old body always there” (James,
2014, p. 134). However, in the past decade, researchers have been able to carry out a large amount of research into body ownership thanks to a technique published by Botvinick and Cohen (
1998). There, they showed that it is possible to induce a feeling of body ownership over an artificial hand by combining the visual stimulation of the prosthetic rubber hand with synchronous tactile stimulation of the participant’s own hand. The resultant feeling of ownership over the rubber hand has led to this paradigm being known as the “rubber hand illusion” (RHI). This effect demonstrates that the experience of one’s body as one’s own depends upon the brain’s ability to compare and integrate signals from different senses in a probabilistic manner (Apps & Tsakiris,
2014; Limanowski & Blankenburg,
2013). In the case of the RHI, the brain detects the synchrony between the felt touch on the real hand and the seen touch on the rubber hand and infers from this matching that the felt touch must originate from the observed hand leading to the feeling of ownership over that hand.
Since the discovery of the RHI, researchers have demonstrated that the integration of other body-related senses can also produce an illusory body ownership. These include: visual-motor synchrony, in which participants observe a hand moving in synch with one’s own (Dummer, Picot-Annand, Neal, & Moore,
2009; Riemer, Kleinböhl, Hölzl, & Trojan,
2013; Walsh, Moseley, Taylor, & Gandevia,
2011); tactile-motor synchrony in which touching a fake hand while one’s own hand is touched leads to the perception that the participant is touching their own other hand (Lopez, Bieri, Preuss, & Mast,
2012; White, Davies, & Davies,
2011); the “rubber voice illusion” (Zheng, Macdonald, Munhall, & Johnsrude,
2011) in which hearing a stranger speaking while saying the same words one’s self led participants to experience the others voice as a distorted version of their own; between synchronous vision and pain stimulation (Capelari, Uribe, & Brasil-Neto,
2009); and by synchronising the rhythm of visual flashes on the fake hand to the rhythm of participants’ heartbeat. These last two are particularly important, as they involve the integration of an interoceptive signal (pain, or implicit awareness of the heartbeat) with an exteroceptive signal (vision). This lends support to models of self-awareness which make a link between representations of the internal state of the body and the bodily self (Craig,
2003; Damasio,
1999; Seth et al.,
2011).
Further research has now extended the scope of body ownership, showing that synchronous visual-tactile stimulation can also generate illusions of ownership over other body parts in addition to the hand. For example, synchronous visual-tactile stimulation between one’s own face and that of another can lead to an illusion of ownership over the other’s face, as well as intriguing changes in the perceived similarity of that face to one’s own (Sforza, Bufalari, Haggard, & Aglioti,
2010; Tsakiris,
2008). Furthermore, body ownership illusions are no longer restricted to individual body parts; a “full-body illusion” has been developed, in which participants feel that they are embodied in a different spatial location to that of their own body (Ehrsson,
2007; Lenggenhager, Tadi, Metzinger, & Blanke,
2007) and even that they have swapped bodies with another person (Petkova & Ehrsson,
2008). These full-body illusions can also be generated by virtual reality, via visual-motor synchrony leading to embodiment of an avatar (Slater, Perez-Marcos, Ehrsson, & Sanchez-Vives,
2009).
By combining these methodologies with neuroimaging techniques, it has been possible for cognitive neuroscientists to identify the brain areas that are integral for generating the sense of body ownership and which may be fundamental for the representation of the bodily self. These studies have revealed a network of uni- and multisensory brain regions that appear to play a role in the experience of body ownership. Some of these areas appear to reflect the specific properties of the body part being stimulated, for example, experiencing synchronous stimulation on the face leads to activation in face specific regions of the inferior occipital gyrus (Apps, Tajadura-Jiménez, Sereno, Blanke, & Tsakiris,
2015), while stimulation of the hand or whole body leads to activation in a visual region that is sensitive to non-face body parts (Ionta et al.,
2011; Limanowski, Lutti, & Blankenburg,
2014). However, multisensory regions have also been identified which show sensitivity to the manipulation of body ownership, including the temporal–parietal junction (TPJ) (Ionta et al.,
2011; Tsakiris, Costantini, & Haggard,
2008), the dorsoanterior insula (Ehrsson, Spence, & Passingham,
2004; Limanowski et al.,
2014), the posterior insula (Tsakiris, Hesse, Boy, Haggard, & Fink,
2007) and the premotor cortex (Bekrater-Bodmann et al.,
2014; Ehrsson et al.,
2004; Petkova et al.,
2011; Tsakiris et al.,
2007).
The findings of the involvement of both the TPJ and insula in the processing of the bodily self are of interest in terms of linking the bodily self to more socially and affectively relevant forms of self-representation as both have been associated with social and emotional cognitive processes. The TJP is activated during perspective taking and thinking about others (Carter & Huettel,
2013; Santiesteban, Banissy, Catmur, & Bird,
2012). The relationship between self-representation and the insula is more complex. Several recent meta-analyses of the insula (Chang, Yarkoni, Khaw, & Sanfey,
2013; Deen, Pitskel, & Pelphrey,
2011) have suggested evidence for a tripartite division between three areas: a posterior region (PI) which is thought to be a key hub for integrating booth internal and external signals relating to the body (Craig,
2009); a ventroanterior region (vAI) which is the region most strongly linked to the processing of emotional (Morita et al.,
2013; Sanfey, Rilling, Aronson, Nystrom, & Cohen,
2003) and social information (Lindner et al.,
2013; Xiang, Lohrenz, & Montague,
2013); and a dorsoanterior region (dAI) involved in higher-level cognitive processing such as attention (Eckert et al.,
2009). However, despite these functional differentiations, it is important to note that these areas show significant reciprocal connections between them with signals about the body processed in PI feeding into social–affective processing in vAI and into conscious awareness via attentional processing in the dAI (Craig,
2009; Simmons et al.,
2013).
Conceptual Self
The conceptual self is generally thought to be made up of one’s attitudes and beliefs about one’s values, preferences, past experiences and social roles (Kuhl, Quirin, & Koole,
2015). In contrast to the bodily self, the conceptual self is thought to emerge gradually during development via the association and organisation of intra- and interpersonal information closely related to one’s behaviour and goals into a coherent network of self-relevant associations (Markus & Wurf,
1987; Perugini & Leone,
2009). The formation of the conceptual self relies on our interactions with others, particularly through linguistic and cultural identification (Gallagher,
2000; Gawronski & Bodenhausen,
2006; Goffman,
1959; Mead,
1913,
1935; Neisser,
1991). In addition, the fact that the conceptual self is closely associated with autobiographical memories means that it plays a central role in the maintenance of personal identity over time (Charlesworth, Allen, & Havelka,
2016; Damasio,
1999; Prebble, Addis, & Tippett,
2013).
Social interaction appears to play a clear role in the development of the conceptual self. This aspect has been addressed by Nelson (
2003), who has detailed how, as children begin to learn language, they are taught by caregivers to narrate the events of their lives. These narratives begin by being highly localised and simplistic, requiring a large amount of prompting from the care giver, e.g. “What sort of animals did you see at the circus?” (Fivush & Nelson,
2006). However, over time children learn to develop these narratives on their own, which adds a new awareness of self in past and future experiences. This also allows them to develop the ability to contrast their own past and future self-narratives to those of others.
The type of scaffolding that the child receives plays a key role in shaping distinct variations in self-perception across culture and gender. For example, parents tend to be more elaborative when developing narratives with daughters than with sons which may explain why by their fourth year girls talk more about feelings and thoughts in personal experiences than boys (Fivush,
2011). Fivush and Nelson (
2004) argue that the cultural differences in conceptions of selfhood between Western and Eastern cultures (for reviews see Cohen, Leung, & Hoshino-Browne,
2007; Markus & Kitayama,
2010) can be traced back to differences in the way that carers in the West and East support their children in developing narratives in autobiographical memory. They note findings that mothers from Western cultures talk about the past in more elaborate and emotional language and tend to focus on the child’s own experience of events while mothers from Eastern cultures tend to emphasis the communal setting of events and to highlight the moral emotions and lessons that emerge from experiences (Leichtman, Wang, & Pillmer,
2003). These differences in the style of scaffolding appear to continue across life with both older children and adults from Western cultures tending to have more detailed, elaborate and emotional narratives of their past than their counterparts in Eastern cultures (Pillmer,
1998).
Research in neuroscience on the conceptual self has largely focused on comparing neural activity when people are viewing stimuli related to self (e.g. self-relevant traits, own name, own face, autobiographical memories) as opposed to stimuli related to others. Several key regions along the cortical midline appear to show greater activation to self-related stimuli than other-related stimuli (Heatherton,
2006; Northoff et al.,
2006; Northoff, Qin, & Feinberg,
2011), including the anterior cingulate cortex (Leshikar, Cassidy, & Gutchess,
2016), the medial prefrontal cortex (mPFC) and the vAI (Murray, Debbané, Fox, Bzdok, & Eickhoff,
2015). The mPFC is particularly involved in the processing of information about people’s traits, preferences and beliefs (Frith & Frith,
2003; Ma, Baetens, Vandekerckhove, Van der Cruyssen, & Van Overwalle,
2013; Schilbach,
2015) and shows sensitivity to a number of social factors including social status and ostracism (Muscatell et al.,
2012; Powers, Wagner, Norris, & Heatherton,
2013). Importantly, there is now considerable evidence for a ventral dorsal split within the mPFC, with the ventral region (vMPFC) showing greater involvement in the processing of self-relevant traits, while the dorsal region (dMPFC) is involving in processing the traits of dissimilar others (Araujo, Kaplan, & Damasio,
2013; Denny, Kober, Wager, & Ochsner,
2012; Mitchell, Macrae, & Banaji,
2006; Moore, Merchant, Kahn, & Pfeifer,
2014; Powell, Macrae, Cloutier, Metcalfe, & Mitchell,
2010).
Further evidence for the role of the vmPFC in representing the conceptual self comes from studies showing cultural differences in vmPFC activation during self-processing. Zhu, Zhang, Fan, and Han (
2007) scanned Western and Chinese participants while thinking about either their own traits, their mother’s traits or a politician’s traits. They found that while Western participants showed vmPFC activation only when thinking about themselves, Chinese participants, whose culture emphasises the interdependent nature of the self, showed mPFC activation in both the self and mother conditions suggesting that their brains were processing their mother’s traits as self-relevant. A follow-up study showed that when students from Hong Kong, who can be considered bicultural due to the long period of British rule, are primed with Western identities they showed increased vmPFC differentiation between self and mother compared to when they were primed with Chinese identities (Ng, Han, Mao, & Lai,
2010). Similar modulations of vmPFC activity have also be seen between Chinese students in America who have become less interdependent since arriving compared to those who became more interdependent (Chen, Wagner, Kelley, & Heatherton,
2015). In addition, Chiao et al. (
2009) showed that across cultures those with a more independent view of the self showed greater mPFC when thinking about general self-traits, e.g. “I am truthful”, while those with an interdependent view of the self showed greater mPFC when thinking about contextual self-traits, e.g. “When talking to my mother I am truthful”. The vmPFC has also been shown to have greater activation to objects owned by the participant (Kim & Johnson,
2012), suggesting a role in representing an extended “material” self as well as an extended social self.
In addition to holding information about self-relevant traits, preferences, etc., the conceptual self is also thought to strongly rely on autobiographical information stored in episodic memory. Meta-analyses of imaging studies have shown that autobiographical memory tasks recruit similar vmPFC areas to self-trait processing along with a number of other brain areas including the hippocampus (Spreng, Mar, & Kim,
2009; Svoboda, McKinnon, & Levine,
2006). Furthermore, a recent study examined functional connectivity between the hippocampus and neocortex during the retrieval and elaboration of episodic memories and found that while the dmPFC is functionally coupled to the hippocampus during the retrieval of memories the vmPFC strongly coupled to it both during retrieval and when participants are required to relive the memory in elaborate detail (McCormick, St-Laurent, Ty, Valiante, & McAndrews,
2015). These results further demonstrate the importance of the vmPFC to the processing and experience of the conceptual self.
Integrating the Bodily and Conceptual Self
Until recently, there have been few attempts to consider the relationship between the bodily and conceptual self, or how the brain’s representations of the bodily and conceptual selves interact. Farmer and Tsakiris (
2012) suggested one possible branch between the two forms of selfhood by outlining the concept of a bodily social self, which is the first form of selfhood in which one’s self is represented as an object of others’ perceptions. The development of the bodily social self is closely entangled with the ability to represent others as having their own perspective, separate from one’s own. This form of selfhood is also still considered ultimately bodily as, at least in its developmentally primitive form, it is thought to first rely upon recognising the commonality of one’s own body to those of others. A similar tripartite distinction has been made by Sugiura (
2013) who distinguishes between three different self-schemas: the physical self-schema which roughly corresponds to the bodily self described here; the interpersonal self-schema which emerges due to social interaction and processes how the self is perceived by other individuals; and the social-value self-schema which processes a more general sense of the self relative to others and is involved in the ascription of traits and social roles to the self. This social-value self roughly corresponds to the conceptual self as discussed in this article. Importantly, both of these two models of the self allow for cross-talk between the different forms of self-representation, which can allow changes in one form of self-representation to affect changes at another level in a hierarchical manner (see Feinberg,
2011 for an additional tripartite hierarchical model of the self).
In terms of neural links between bodily and conceptual self-representation, so far there have been few direct attempts to understand how the neural regions involved in the bodily self and the conceptual self influence each other. However, one recent meta-analysis of fMRI studies sought to identify common regions activated both when participants perceived their own face and when the saw self-relevant traits (Hu et al.,
2016). The authors found that the only regions to show an overlap in activation across both tasks were the dorsal anterior cingulate and the vAI, suggesting that these regions may play a key role in specifying self-relevance across different domains. The finding of vAI activation is of particular significance given its role in processing interoceptive signals (Craig,
2009) and the role of the AI more generally in the processing of body ownership (Ehrsson et al.,
2004; Limanowski et al.,
2014). It should be noted, however, that the sense of bodily self used by Hu et al. related to the recognition of one’s own face from the outside and as such significantly differed from the sense of the bodily self described above which is grounded in the ongoing multisensory perception of bodily signals from both interceptive and exteroceptive senses rather than mere recognition of visual representations of the self. As such, it is still unclear whether there is any specific brain area that is directly involved in processing all self-related information, or if the different types of neural self-representation interact with each other through connections between distinct networks.