Many people with schizophrenia experience an altered sense of self, meaning that they feel as if someone else is controlling their actions. Scientists have determined that this sensation — which is described as a deficit in the “sense of agency” — is associated with problems in sensorimotor brain signals.
In a new study, scientists at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland wanted to take this further and investigate another unexplored category in the field of schizophrenia: the “sense of body ownership,” essentially the feeling that our bodies belong to ourselves. Their findings, however, suggest that body ownership is not affected in schizophrenia.
“It is important to publish such ‘negative’ results,” said Professor Michael Herzog. “Otherwise, we give the impression that schizophrenia patients are deficient in all paradigm tests — which, as our study shows, is simply not true.”
For the study, the researchers evaluated 59 patients with chronic schizophrenia and compared them to 30 healthy people. The participants completed a well-established test called the “Full-Body Illusion,” developed in the lab of Professor Olaf Blanke at EPFL.
The idea behind the Full-Body Illusion is to induce changes in body ownership through prolonged multisensory stimulation. For example, participants in the study had their real backs stroked while they watched their virtual backs being stroked through a virtual reality visor.
When both real and virtual stroking occurred at the same time, the participants typically experienced a stronger sense of body ownership and identification with the virtual body, while they also felt like they were drifting towards it. But when the strokes were not synchronized, the patients felt none of this.
The researchers found that the schizophrenia patients reacted the same way as healthy controls in the Illusion, meaning that their sense of body ownership was unaffected by schizophrenia.
“This has never been shown or reported before,” said study leader Albulena Shaqiri. “Up to now, it was believed that schizophrenia patients have a disturbed sense of body ownership.”
Schizophrenia patients are known to be impaired in their sense of agency, which has to do with the feeling of being the author of one’s actions. This is caused by problems with sensorimotor mechanisms in the brain, which essentially disrupts the patient’s ability to tell apart self-generated actions from those caused by external sources.
But until now, the question of body ownership has been left open. This is important because agency and body ownership are the two main parts of what we call the Self, and this is the area where schizophrenia manifests.
“This study suggests that body ownership is not affected in schizophrenia,” said Blanke. “Yet, more work is needed to test important aspects of self-consciousness in schizophrenia, such as the many different forms of body ownership — hand, torso, face — their dependency on different multisensory stimuli, and their relation to sensorimotor aspects of self-consciousness such as agency.”
The study is published in the journal Schizophrenia Bulletin.