CALIFICACIÓN DE LA SEGURIDAD DEL PACIENTE

Neurological disturbances of the perception of the own body are multifaceted syndromes, including ownership and agency abnormalities. The involvement of structures like the premotor, posterior parietal cortex (in particular inferior parietal regions) and the insula in pathologies affecting the perception of the body like anosognosia or asomatognosia has been confirmed by a number of studies (Baier & Karnath, 2008; Berti et al., 2005; Karnath & Baier, 2010; Orfei et al., 2007; Zeller, Gross, Bartsch, Johansen-Berg, & Classen, 2011). At the same time we know that these structures are involved in the generation of ownership and agency (Brozzoli et al., 2012; Ehrsson et al., 2004; 2005; Farrer et al., 2003; Farrer, Frey, Van Horn, Tunik, Turk, et al., 2008b; Tsakiris et al., 2007a). The question arises how and where these aspects interact at the neural level when we perceive our own body moving. The present results might help to further clarify the exact relationship between ownership and (internal and external) agency also at a neural level by examining these functions with imaging techniques like fMRI or EEG. These insights could further elucidate these pathologies and help us to understand why patients exhibit certain pathologies. This could also elucidate why, for example, anosognosia and asomatognosia co-occur after lesions in the insula (Baier & Karnath, 2008), but anosognosia appears after lesions in the premotor cortex (Berti et al., 2005). A deeper investigation of ownership and agency at a behavioral and neural level with healthy participants might help us to better understand these observations in these patients.

The present rubber hand illusion paradigm could be a useful new tool to investigate the breakdown of ownership and agency in psychotic disorders, in particular schizophrenia. A leading hypothesis for a decade has been that some of the symptoms of schizophrenia might be explained by the breakdown in comparator mechanisms related to the sense of agency (Franck et al., 2001; Frith, Blakemore, & Wolpert, 2000b; Haggard, Martin, Taylor-Clarke, Jeannerod, & Franck, 2003; Shergill et al., 2005; Synofzik, Thier, Leube, Schlotterbeck, & Lindner, 2010; Voss et al., 2010), resulting in delusions of control and passivity symptoms (Frith, 2005a; 2005b; Jeannerod, 2009). Recently schizophrenia researchers have also started to investigate the domain of body-ownership and possible impaired mechanisms of body representation by using the rubber hand illusion paradigm (Germine et al., 2012; Peled et al., 2000; Thakkar et al., 2011). Having said that the question arises how these disturbances of agency and ownership might interact to eventually result in the problems of self-recognition seen in psychotic disorders. Given that psychotic patient do not only have a distorted experience of agency, but also ownership (Waters & Badcock, 2010).

From this perspective the present moving rubber hand illusion set-up could be a useful new approach for cognitive schizophrenia research to combine measurements of ownership and agency in a single paradigm and further explore how psychotic traits affect the experience of the own body or vice versa. As illustrated by Study IV not only psychotic patients, but also delusion-prone participants might already exhibit certain abnormal tendencies in their experience of their body. An interesting question can be formulated by asking whether self-recognition disturbances seen in schizophrenia are a result of changes in ownership and / or agency, and how both these processes interact when prodromal individuals converge to a clinically manifest psychosis. Future research could explore the factors behind psychotic disorders by using bodily illusions like the moving rubber hand, which tap more specifically into the mechanisms of self- recognition by combining ownership and agency.

7.4.2 Research on neuroprosthetics

Recent years have seen increasing interest in how one could design advanced prosthetic limbs that would feel and act more like real limbs. These limbs could be controlled by brain-computer interfaces (Hochberg et al., 2006; Nicolelis, 2003; Schwartz, 2004; Velliste, Perel, Spalding, Whitford, & Schwartz, 2008), myo-electrically controlled

(Marasco, Kim, Colgate, Peshkin, & Kuiken, 2011), or be traditional cosmetic prostheses (Ehrsson et al., 2008). Regardless of the technical design and degree of invasiveness it seems reasonable to assume that the user would benefit from experiencing both ownership and agency of the artificial limb. The basic cognitive and neuroscientific constraints of ownership and agency, as explored here, could thus be taken into account when developing the next generation of advanced prosthetic devices. That these insights from non-amputated participants can be transferred to the amputees is seen by the fact that the rubber hand illusion can be induced in amputated participants. The tactile stimulation is applied here at the place of the stump where the participants report a referred sensation to one of the digits, and to the corresponding digit of the rubber hand. Similar to non-amputated participants also amputees report similar sensations of ownership after synchronous, but not asynchronous stimulation (Ehrsson et al., 2008; Rosén et al., 2009; Schmalzl et al., 2011). A case study using fMRI suggests that also in these participants a premotor-posterior parietal network is activated during the illusion (Schmalzl, Kalckert, Ragnö, & Ehrsson, 2013).

A critical step here is the development of sensory feedback from the prosthesis. Sensory feedback is necessary to create a sense of ownership towards the artificial limb, but equally important for motor control (Johansson & Flanagan, 2009). Also here recent technological advances in providing such tactile feedback offer promising new developments (see i.e., Raspopovic et al., 2014), which can lead to a new form of prosthetic devices in the not so distant future. Once these technological advances will become part of general therapeutic strategies in the care of amputated patients, the experience of ownership and agency towards the prosthesis would help the user´s overall well being. These experiences might restore a more complete and coherent perception of the own body and increase acceptance of the prosthesis (P. Gallagher & MacLachlan, 1999).

Similarly the present results could be useful to optimize the sense of ownership and agency in virtual-reality to give people simulated limbs and bodies (Slater et al., 2008; Slater et al., 2009; Perez-Marcos et al., 2009; Sanchez-Vives et al., 2009). These techniques create new avenues in the therapeutic and rehabilitative strategies for patients with physical or psychological disorders related to their experience of the body or self (Sanchez-Vives & Slater, 2005).