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 suffering from pain conditions, especially in the case of chronic pain. One way of modulating the perception of pain through the perception of body image is through the use of interventions based on visual feedback. In this regard, some studies have highlighted the possibility of reducing the perception of pain in healthy and clinical populations with the use of "illusions" of one's own body created through immersive virtual reality. For example, through the use of synchronous visual-tactile multisensory stimulation on one's own face / body and on that of others (fake body), is possible to induce illusions of self-recognition in other fake bodies. In the case of the face, this type of illusion of belonging of other faces is commonly known as the "enfacement illusion", through which is possible to change or modulate the self-representation, with important implications for all those subjects who have distorted body representations, such as patients suffering from chronic pain. The main goal of the present protocol is to evaluate the effects of an experimental treatment based on enfacement illusion on the perception of pain (VAS scale) with respect to a control condition (pleasant virtual environment exposure). The secondary objective is to study any correlations between pain and body image, personal, clinical and psychological intrapersonal variables. One-hundred patients with chronic headache will be randomly assigned to the two conditions: experimental group (based on the "enfacement illusion") and control group (exposed to a pleasant virtual environment). Both conditions include an immersive virtual reality treatment of 3 sessions of 15 minutes each, during one week.

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.

In this frame, the primary goal of this double-blind randomized controlled trial is to assess whether the "enfacement illusion" of representing oneself (inducing the sense of ownership) in a happy face through an immersive virtual reality may reduce the perception of pain in patients with chronic migraine. A secondary goal is to evaluate the effects on the perception of one's body image and on the affective and emotional state of a treatment based on "enfacement illusion" with respect to a control condition. Both treatment protocols consist of 3 session/week, 15 minutes/day, of the virtual reality enfacement illusion exposure vs pleasant virtual environment exposure. Female patients with chronic migraine accomplishing the clinical characteristics included in the ICHD-III version for chronic migraine, with pain perception between 20 and 80 on a 0-100 visual analogue scale will be recruited from Headache Science center Unit of IRCCS Mondino Foundation.

All patients will undergo the following assessment measures:

Pre / post treatment (T0-T1): all subjects will be assessed as regards their affective and emotional state with: Body Satisfaction Scale (BSS), Hospital Anxiety and Depression Scale (HADS), Emotive Regulation Questionnaire (ERQ) , and the Difficulties in Emotion Regulation Scale (DERS), Pain-Visual Analogue Scale (VAS), Body Image Questionnaire (BIQ), and Positive and Negative Affect Schedule (PANAS).

Pre / post visual exposure session: all subjects will be assessed with the Pain-Visual Analogue Scale (VAS), Body Image Questionnaire (BIQ) and Positive and Negative Affect Schedule (PANAS).

After each visual exposure session: the patients of the experimental group will fill in a questionnaire relating to the level of sense of belonging (embodiment) of the virtual body. The control group will fill out a questionnaire relating to the level of immersion in the virtual environment.

Inclusion Criteria:

1. Accomplish the clinical characteristics included in the ICHD-III version for chronic migraine.
2. Age between >18 to 65 year old (only women).
3. Previous history of migraine as primary headache.
4. Pain perception between 20 and 80 on a 0-100 VAS.

Exclusion Criteria:

1. Dementia, epilepsy, psychosis, mental retardation, pregnant and breastfeeding women.
2. Visual problems

There are studies reporting differences in pain perception between man and women (Wiesenfeld-Hallin, 2005)