the body in the brain

background

You may be familiar with Botvinick and Cohen’s famous 1998 experiment with the illusion of a rubber hand, which showed that people can feel sensations of touch on a prosthetic hand when their actual hand is covered on a table next to them (BBC Experiment explains over here). The study provided an early indication that the way we define what is and what is not “our body” may involve a multisensory interaction between vision, touch, and perception (spatial perception). However, this idea is that the way we define what is our The body may be affected by our still-controversial flawed and “deceptive” senses.

Moving forward a few years later, the creation of immersive virtual reality (IVR) technology has allowed users to feel that they are physically present in a digital landscape by interacting with it as a digital avatar. As in rubber hand deception, users report Strong deceptive feelings Ownership of these “artificial” objects. In the world of neuroscience, researchers have become fascinated by these effects, which have come to be known as “illusions of body ownership.” previously, Clinical Applications Delusions of body ownership have emerged to treat neurological disorders, and a central question remains: Where does this powerful sensation come from?

Studying in depth

Looking ahead to the illusion of a rubber hand, a new study by UCL’s Elias Casula Show the potential origins and mechanisms of body ownership in the brain by integrating IVR and neuroimaging technology. Study participants sat with their hands covered on the table in front of them, and watched as a prosthetic arm and hand could be ‘moved’ in the IVR, all while transcranial magnetic stimulation (TMS) was used to stimulate the ‘hand area’. ‘From the participant’s left primary motor cortex.

The primary motor cortex of the brain is primarily responsible for the corresponding muscle movement, which means that stimulating the hand control area in the left skeleton increases the activity of neurons associated with moving the right hand/arm. During this procedure, electrical activity in the brain was monitored using an electroencephalogram (EEG) attached to the scalp.

In an astonishing turn, the results of Casola’s study suggested the existence of a dynamic network in the brain behind the feeling of being embodied in a prosthetic. Within 30 milliseconds of the first TMS pulse, a rapid decrease in initial primary and motor activity was detected. This is likely because our attention has shifted to the “new party” that we can see in the IVR.

After 250 ms, increased activity in the posterior parietal cortex followed. Participants who reported a stronger feeling of owning the hand/arm were positively associated with greater activation in this brain region.

This is very important, as the posterior parietal cortex of the brain is involved in attention/spatial perception and eye movement control. Activation in this brain region indicates that the mechanisms of touch, proprioception and sight All Involved in creating a sense of ownership of the body. It is identified as an anterior-parietal mesh, and it confirms the conclusions made in Botvinick and Cohen’s 1998 Rubber Hand Illusion.

Importantly, this study expands our current understanding of how the brain interacts with illusions of body ownership, clarifying neural plasticity and the role of the primary motor cortex in this process.

Of course, some caveats must be mentioned: fifteen participants were needed to establish statistical significance in this study, and although nineteen years were involved in the historical study, we must treat with caution before taking it as representative of the general population. Further investigation is still required to quantify the extent to which neural activity differs across a broader demographic, particularly among the divergent neural community. for example, Autistic individuals They often respond differently to the illusion of a rubber hand.

The strength of the illusion felt during the IVR experience was also reported through questionnaires, biasing due to the subjective nature of the questions about ownership ‘feelings’. Although these qualitative results are still valuable, they should not be considered definitive. Using TMS to stimulate neurons in the brain also comes with limitations in accuracy, as results can also be affected by other off-target areas that the EEG has not been able to identify. However, in general, it is an important step towards understanding illusions of body ownership and spreading the use of IVR.

Recent studies have already documented the enormous potential therapeutic applications of IVR delusions for those with body malformation; some Anorexia patients in the Netherlands They experienced lasting improvements in the subjective perception of their body size after being subjected to full-body VR illusions of varying sizes. It appears that creating the illusion of ownership of the body and altering aspects of it, such as size, transparency and realism, may allow the formation of new neural pathways in the brain. a meta استعراض review It found that for those with pain and chronic pain conditions, including patients with phantom limb pain, nerve injuries, osteoarthritis, and complex regional pain syndrome, their average pain rating was reduced by half after they underwent virtual limb treatments.

Previously, we thought of the sensory ‘body schema’, or the physical sense of ourselves in space, as distinct from the conscious evaluative ‘body image’, which represents how we perceive or feel about our bodies. However, the use of illusions of ownership of the body to treat disorders is considered traditional Both Increasingly, “mental health” and “physical health” issues indicate that this is not the case. Casula’s study is exciting because it supports the idea of ​​a ‘single body’ in the brain, with ‘body image’ and ‘body schema’ as an interconnected matrix. This shift represents a change in the way we think and treat various neurological disorders.

Therefore a better understanding of the neural mechanisms underlying body ownership is critical to allow better use of IVR in healthcare settings.