Changing Body Representation Through Full Body Ownership Illusions Might Foster Motor Rehabilitation Outcome in Patients With Stroke

Abstract

How our brain represents our body through the integration of internal and external sensory information so that we can interact with our surrounding environment has become a matter of interest especially in the field of neurorehabilitation. In this regard, there is an increasing interest in the use of multisensory integration techniques-such as the use of body ownership illusions-to modulate distorted body representations after brain damage. In particular, cross-modal illusions such as mirror visual feedback therapy (MVFT) have been widely used for motor rehabilitation. Despite the effectiveness of the MVFT for motor rehabilitation, there are some limitations to fully modify the distorted internal representation of the paretic limb in patients with stroke. A possible explanation for this relies on the physical limitations of the mirror in reproducing upper-limb distortions, which can result in a reduced sense of ownership of the mirrored limb. New digital technologies such as virtual reality (VR) and 360° videos allow researchers to create body ownership illusions by adapting virtual bodies so that they represent specific morphological characteristics including upper-limb distortions. In this manuscript, we present a new rehabilitation approach that employs full virtual body ownership illusions, using a 360° video system, for the assessment and modulation of the internal representation of the affected upper limb in stroke patients. We suggest modifying the internal representation of the upper limb to a normal position before starting motor rehabilitation training.

Virtual Body Ownership Illusions for Mental Health: A Narrative Review

“…One example is a study by Matamala-Gomez and colleagues (2019) [ 70 ], who investigated how altering the visual appearance of the painful virtual arm, in terms of size (big, normal, small) and transparency (0%, 25%, 50%, 75%) modulated pain perception in two different groups of chronic arm pain patients (CRPS and peripheral nerve injury (PNI)). Interestingly, in contrast to a study conducted on healthy subjects [ 59 ], Matamala-Gomez et al (2019) [ 70 ] found that increasing the transparency of the observed virtual arm decreased pain ratings in patients with CRPS, but this did not occur in those with PNI. On the other hand, increasing the virtual arm size slightly increased pain ratings only in CRPS patients.…”

“…Today, VR is considered an advanced form of human-computer interaction that allows participants to act, communicate, and become present in an immersive computer-generated virtual environment [ 1 , 91 , 107 ]. Taking advantage of the potential of VR technology, a large number of studies have demonstrated that the sense of embodiment of a virtual body experienced during virtual BOIs can be exploited as a powerful tool for modulating some clinical disorders (e.g., motor, pain, or psychological and psychiatric disorders) by inducing changes in the patients’ internal body representation [ 59 , 61 , 70 , 108 , 109 , 110 , 111 ].…”

“…The mismatch between the internal distorted representation of the body part and the observed reflection of the body part in a normal position could reduce the feeling of ownership of the reflected body part, thus reducing the effectiveness of the therapy. In this regard, VR enables the possibility to induce embodiment of a full virtual body observed from a first-person perspective [ 50 ], and the manipulation of morphological characteristics of the represented virtual body [ 59 , 60 ]. Moreover, using virtual BOIs it is possible to go beyond the mirroring of movement performed with the healthy hand.…”

“…Currently, the most widely used BOI for motor recovery in patients with motor disorders is MVFT [ 76 ]. Nevertheless, even though the effectiveness of MVFT to modulate body representation and to improve motor recovery after stroke has been largely demonstrated [ 81 , 82 , 83 , 84 ], there are still some physical limitations to inducing a good enough sense of ownership and full embodiment over the observed body (part) in the mirror, which may weaken the rehabilitation outcome [ 59 ]. Hence, the development of VR systems through which it is possible to induce embodiment of a full virtual body observed from a first-person perspective [ 50 ], and therefore to manipulate morphological characteristics of the represented virtual body [ 48 , 56 ] as well as the visuo-motor mapping between the real and the virtual body, offers a potential powerful alternative to the traditional MVFT [ 85 ].…”

“…The possibility to adapt the virtual body representation to the specific characteristics required by researchers or clinicians makes virtual BOIs a powerful tool to study and modulate altered body representations. In this regard, several studies have shown that through the use of humanoid virtual BOIs, people can experience ownership over virtual bodies of a different gender [ 49 ], age [ 54 , 55 ] or skin colors [ 56 , 57 ] having a different posture [ 56 , 58 , 59 ], an altered size of some body parts [ 45 , 60 , 61 ], or a certain degree of transparency of the virtual body [ 62 ]. As we review below, such changes in body representation, possible through virtual BOIs, not only modulate internal body representations but can also affect participants’ behavioral and physiological responses such as their perception of pain [ 63 ], motor learning [ 64 ], and cognitive and responses [ 65 , 66 ].…”