Generalized Anxiety Disorder (GAD) is a psychiatric disease characterized by long-lasting anxiety that is not focused on a specific object or situation. According to the DSM-IV-TR the essential feature of GAD is at least six months of "excessive anxiety and worry" about a variety of events and situations. Anxiety and worry are often accompanied by a variety of physical symptoms like restlessness, being easily fatigued, difficulty concentrating, irritability, muscle tension and disturbed sleep. The high prevalence of GAD in the general population and the severe limitations it causes point out the necessity to find new strategies to treat it in a more efficient way. Within the treatment of GAD, physical (relaxation and controlled breathing), behavioral (visualization and controlled exposure) and cognitive control strategies (challenging negative thoughts) represent a key part of the treatment, even if they are hard to be learned. Given the features of this disease and its pervasive effect on patient's personal, occupational and affective life, we thought it could benefit from an ubiquitous treatment.We suggested, then, to improve the treatment of GAD through the use of a biofeedback enhanced virtual reality (VR) system used for relaxation, controlled exposure and SIT. The use of SIT in the context of GAD is motivated by the acknowledgment that sometimes stressors can't be avoided or altered and then patients can't apply strategies focused on finding solutions. In these instances, coping effort should be directed to emotionally palliative set of responses such as acceptance, reframing and perspective thinking. All these cognitive changes are facilitated if a concomitant relaxation is induced. The treatment involves two virtual reality components:

I) an immersive virtual reality system experienced in the therapist's office;

II) a mobile exposure system allowing patients to perform the virtual experience in an outpatient setting. The role of the mobile exposure system is the following:

• To present and structure emotionally relevant contents in an ubiquitous context.
• To verify the compliance of the patient and eventually alert patient/therapist;
• To track in real-time the emotional level of the patient and record it for later assessment by the therapist;
• To provide a feedback to the patient able to help him in coping with the contents;
• To automatically contact the therapist if the emotional level is higher than a preset cut-off value defined by the therapist.

The patients were randomly assigned to the following groups: (1) the VR and Mobile group (VRMB) including biofeedback - 7 subjects; (2) the VR and Mobile group (VRM) without biofeedback - 9 subjects; (3) the waiting list (WL) group - 8 subjects:

1. Virtual Reality + Mobile Phone without Biofeedback Condition (VRM). In this experimental condition patients received an eight-session VR-based treatment including relaxation and exposure. In sessions 1 to 6, the patient explored a beautiful VR tropical island (experienced with a head-mounted display and head-tracking) following a predefined path leading to different relaxing areas: Campfire, Beach and Waterfall. In these areas the patients started to relax by observing the flickering campfire, watching waves lapping gently on a shore, or looking to the waterfall and fish pond. Each experience was supported by an audio narrative based on progressive muscle relaxation and/or autogenic techniques. All the environments were developed by the ESIEA INTREPID team (J.L. Dautin, J. Ardouin, F. Crison and M. Le Renard -www.esiea.fr) using the 3DVIA 4.1 Virtools toolkit by Dassault Systèmes - www.virtools.com.To improve the efficacy of the training and to increase the effects of relaxation, patients experienced at home, using a mobile phone, on a non-navigable version of the same virtual reality environment experienced during the therapy. The patient was asked to train relaxation abilities at least once a day for the entire duration of the treatment following the treatment plan provided by the therapist. In session 7 and 8 the patients explored again the island reaching a Gazebo in which they are exposed to pre-selected words or images related to their personal stressful events. The patients were then asked to use the learned relaxation techniques to cope with them.

2. Virtual Reality + Mobile Phone with Biofeedback Condition (VRMB). The patients experienced the same protocol described above, but with the biofeedback support (see Figure 2). Specifically, in the sessions with the therapist, HR variations were used to modify specific features of the virtual environment:

   1. Campfire (sessions 1-2). HR controls the fire intensity: a reduction of the patient's physiological activation reduces fire intensity until it disappears;
   2. Beach (sessions 3-4). HR controls the movement of the waves: a reduction of the patient's physiological activation reduces the movement of the waves until the ocean becomes completely calm;
   3. Waterfall (sessions 5-6): HR controls the movement of the water: a reduction of the patient's physiological activation reduces the movement of the water until the water flow becomes completely still;
   4. Gazebo (sessions 7-8): HR controls the size of a stressful image or video: a reduction of the patient's physiological activation reduces the size of the stimulus until it disappears. This exercise is designed following the procedure of SIT.

3. Waiting List Condition (WL). This was a control condition, in which patients were included in a waiting list and not received any kind of relaxation training.

Inclusion Criteria:

1. Primary diagnosis of GAD
2. Requesting treatment for their GAD
3. Older than 17 and younger than 70; (4) no change in dose of psychotropic medications 1 month before inclusion

Exclusion Criteria:

1. Depressive disorder preceding the current episode of GAD or requiring immediate treatment
2. Behavior therapy received for their GAD
3. Evidence of organic mental disorders accounting for the complaints, mental retardation, psychotic disorders, alcohol or drug dependence
4. Migraine, headache, seizure disorder, and vestibular abnormalities since they represent significant contraindications for the use of VR.