ReviewMechanisms underlying embodiment, disembodiment and loss of embodiment
Introduction
The ownership and embodiment of one's body is a seemingly trivial aspect of the self that is nevertheless essential for successful interaction with external objects and people. However, complex mechanisms underlie the maintenance of internal representations of the body (body schemata), body ownership and embodiment. In particular, embodiment is a complex phenomenon that extends from self-embodiment to the embodiment of habitually used tools, prostheses or rubber limbs that effectively extend or displace the normal area of influence of body parts. This paper reviews the neural and sensory mechanisms underlying bodily experience. It then defines the conceptually unique aspects of bodily experience from internal representations of the body and manifestations of the body image and body schema, to body ownership and dis-ownership, and embodiment and disembodiment. It finally reviews some of the techniques by which embodiment can be modified or manipulated; such as through tool and prosthesis use, and rubber limb illusions.
The present review suggests a model whereby embodiment operates both via automatic bottom-up and potentially conscious top-down processes; these permit the establishment, with respect to the body, of sensory–motor and motor–sensory maps of the limbs—and subsequently, tools and prostheses after amputation—whereby they may be optimally deployed in space. The account accommodates a number of otherwise disparate phenomena (such as phantom sensations, rubber limb illusions, unilateral neglect, somatoparaphrenia, and alien limb phenomena), and even suggests that the phantom limb phenomenon may play an adaptive role in certain contexts, rather than being a mere by-product of a disturbed spatial reference system.
Section snippets
Multisensory integration and egocentric frames of reference
Information regarding the body in space is generated via the integration of afferent sensory information relating to the self in space—including retinal, somaesthetic, proprioceptive, vestibular and auditory inputs—together with efferent information relating to motor output and the movement of the body in space, including movement of the eyes, neck, trunk and limbs (Stein, 1992; Ventre-Dominey et al., 2003). Regions within the posterior parietal cortex (PPC) integrate these multisensory inputs
Body representations
Ongoing bodily experience is fundamentally based on internal spatial representations of the body, which were first conceptualised by Münk and Bonnier in 1890 and 1905, respectively (Holmes and Spence, 2006; Maravita, 2006). Head and Holmes (1911–1912), however, made the first major advances in the development of concepts of body schemata. Bodily experience involves a complex integration of (a) automatic, bottom-up sensory and organisational processes (body schema) with (b) higher-order,
Body ownership and self-attribution
The sense of body ownership is defined as the perception that parts of the body phenomenologically and functionally belong to oneself (self-attribution). Body ownership thus stems from the convergence of multiple sensory inputs, particularly proprioceptive and visual inputs. Using the rubber limb paradigm (described below), Ehrsson et al. (2004) identified that the feeling of ownership of a seen limb was associated with premotor cortex activity, and that self-attribution may be related to
Embodiment
Embodiment involves the perception that one's sense of self is localised within one's bodily borders (Arzy et al., 2006c). Embodiment is not confined to the bodily self and may extend, for example, to a habitually used tool or prosthesis that effectively extend the body's area of influence. Embodiment is a complex process that involves representations of the self and the body, multi-sensory integration and motor intention and function. Arzy et al. (2006c) identified that the EBA and TPJ were
Illusory manipulations of self-attribution and embodiment
Body awareness, ownership and perception are modifiable aspects of conscious and unconscious experience. The plasticity of body perception has become apparent through research on visual capture, as well as through evidence of the internalisation of deployed tools, and the convergence between a phantom limb and a prosthesis or an intact limb and a rubber limb. These illusions of embodiment and bodily perception will now be described.
Conclusions
Bodily experience depends upon the integration of multi-sensory information relating to the body in space. Essentially, there are three aspects to bodily experience: (a) internal representations of the body; and the identification with parts of the body that are (b) attributed to the self and “owned”, and (c) embodied by oneself. Body ownership is enhanced through the mechanisms of visual capture that combine proprioceptive and visual information about limb position. Furthermore, predictive,
Acknowledgement
We would like to acknowledge the feedback provided by two anonymous reviewers.
References (205)
- et al.
Effects of prismatic adaptation on judgements of spatial extent in peripersonal and extrapersonal space
Neuropsychologia
(2003) - et al.
Nonpsychotic, nonparaphilic self-amputation and the internet
Comprehensive Psychiatry
(2005) - et al.
Remission of somatoparaphrenic delusion through vestibular stimulation
Neuropsychologia
(1991) - et al.
Coordinates of extracorporeal space
- et al.
Relations between the directions of vibration-induced kinesthetic illusions and the patter of activation of antagonist muscles
Brain Research
(2000) - et al.
Revisiting unilateral neglect
Neuropsychologia
(2006) - et al.
Bodily illusions modulate tactile perception
Current Biology
(2005) - et al.
Chronic phantom sensations, phantom pain, residual limb pain, and other regional pain after lower limb amputation
Archives of Physical Medicine and Rehabilitation
(2000) - et al.
Human vestibular cortex as identified with caloric stimulation in functional magnetic resonance imaging
NeuroImage
(2002) - et al.
Reduced endogenous control in alien hand syndrome: evidence from naturalistic action
Neuropsychologia
(2005)