The Effects of the "Enfacement Illusion" on Pain Perception in Patients Suffering From Chronic Migraine.

The concept of body image can be described as "the intentional content of consciousness comprising perceptions, attitudes and beliefs relating to one's body". Over the years, there has been a growing interest in this topic, highlighting that body image can be distorted in people with pain, especially in the case of chronic pain. In the context of migraine, some studies have shown that the perception of pain can alter both the facial recognition capacity and the visuospatial perception compared to healthy subjects. Furthermore, other studies have shown that by reducing the altered perception of body image in patients with migraine associated with overuse of drugs, it is possible to induce beneficial effects on their affective state and on the perception of pain. One way to modify the perception of pain through the perception of the body image consists in the use of interventions based on visual feedback. Other studies have also highlighted the possibility of reducing the perception of pain in healthy and clinical populations with the use of "illusions" of one's body created through immersive virtual reality. In a pilot study conducted at IRCCS Mondino, the effect of different visual feedback conditions (facial expressions): positive, neutral, negative and white screen (control condition) on the modulation of pain perception in a sample of 38 patients with chronic migraine, demonstrated that the observation of a positive emotional face stimuli, when compared to other conditions, decreased their pain perception. Further, other studies demonstrated that the use of synchronous visual-tactile multisensory stimulation on one's face / body and on that of others (fake body) is able to induce illusions of self-recognition toward the others body part. This illusion of belonging of other faces thus created is known as "enfacement illusion" and seems to be positively correlated to the empathic traits of the subjects mediated by emotion regulation. Other studies show that the "enfacement illusion" seems to be a good strategy for changing the self-representation, with important implications for all those subjects who have distorted body representations, such as patients suffering from chronic pain. This study aims to evaluate whether through the "enfacement illusion" of representing oneself in a happy face exposed through an immersive virtual reality system (experimental group) it is possible to reduce the perception of pain in patients with chronic migraine. This effect would be mediated by an improved body image and empathy for positive emotions. In order to demonstrate the effects of the "enfacement illusion" on their own body representation and pain perception, a control group will be subjected to a positive exposure (pleasant environment) in an immersive virtual environment, which seems to be able to produce distracting effects on pain perception in patients with chronic migraine. It is hypothesized that patients with chronic migraine exposed to the "enfacement illusion" will experience greater pain relief and improve the perception of their body image compared to the control group. Therefore, the present study aims to show a possible relationship between the distortion of the body image and pain perception and, therefore, to demonstrate the effectiveness of the use of "enfacement illusion" as a cognitive behavioral intervention aimed at alleviating pain in clinical populations. Patients in the experimental group will be exposed to the "enfacement illusion" condition, conducted similarly to other studies. In detail, patients will see, through a virtual reality helmet, a virtual body sitting in front of them with a happy face expression. Each session will consist of three phases: (1) habituation to the virtual environment, (2) observation of the virtual facial expression, (3) multisensory stimulations (visuo-tactile stimulation).

Phase (1) habituation to the virtual environment: For approximately 2 minutes the experimenter will ask patients to describe what they see in the virtual environment, as well as the virtual body positioned in front of them.

Phase (2) observation of facial expression: the experimenter will ask patients to focus attention on the face of the virtual body sitting in front of them for about 1 minute.

Phase (3) multisensory with a brush. The multisensory (visual-tactile) stimulation is necessary to induce the sensation of belonging to the virtual body, and specifically to induce the sense of ownership toward the virtual face. The multisensory stimulation will last for 5 minutes.

The control group of this study, will be exposed to a visual stimulation by observing a pleasant immersive virtual reality environment for the duration of 5 minutes. As in the experimental group, in the first 2 minutes of immersion in the virtual environment, the experimenter will ask the patient to describe the virtual environment. Then, the patients will be immersed in the virtual environment for about 5 minutes.