Virtual reality is currently used as a therapeutic strategy in common phobia as agoraphobia or acrophobia, since it permits to have a better control (on occurrence of events or on the environment) during the therapy than in "in vivo" therapy. Our hypothesis here is that we can improves the therapeutic effects of the virtual exposure by giving control to acrophobic patients during their exposure.

The study is based on the exposure of acrophobic patients to virtual environments. During the study, several groups of patients will be distributed according to different conditions: exposure to anxiogenous virtual environments and exposure with the ability to control and secure the anxiogenous virtual environments.

The interest of this project is to improve therapy by exposure to virtual reality. Our project offers a systematic therapeutic approach (using virtual reality and the concept of control) where current therapy are too often approximate. We aim to demonstrate the effectiveness of the control of virtual environments on symptomatic and psychophysiological levels, to evaluate the adoption of these methods in the couple patients-caregivers and also to understand the brain mechanisms (including those prefrontal) involved in this therapy.

Inclusion Criteria of all subjects:

• 18 to 60 years old
• Male or female
• All subjects will be fluent in French.
• Fully informed and freely given, signed Informed consent in written form.
• Patient / Subject affiliated or beneficiary of a social/health security insurance.

Inclusion criteria for acrophobic patients:

• Patients not hospitalized suffering from acrophobia (according to DSM-IV, APA 2000).
• Patients receiving pharmacotherapy (anxiolytics, hypnotics, etc.) may be included provided they are stabilized on treatment for at least 8 weeks.
• Score inferior to 6 at the Behavioural Avoidance Test

Inclusion criteria for healthy volunteers:

• People not hospitalized showing no sign of acrophobia.
• Score superior or equal to 10 at the Behavioural Avoidance Test.

Exclusion Criteria for all subjects:

• Pregnant woman (urine and blood β -HCG test) or lactating (contraindication to PET-scan).
• Women of childbearing potential without effective contraception (contraindication to PET-scan).
• Subject participating in another research evaluating other treatments including a period of exclusion still ongoing.
• Persons under guardianship and adults subject submitted to a measure of legal protection or unable to consent.
• Persons deprived of their liberty by a judicial or administrative decision, those hospitalized without consent under Articles L. 3212-1 and L. 3213-1 that do not fall under the provisions of Article L. 1121-8 and admitted to a health or social institution for purposes other than research.
• People with a non-stabilized diabetes (contraindication to PET-scan).
• Addictions to alcohol or drugs.
• Persons suffering from claustrophobia.
• Contraindications to fMRI.
• People with hearing loss.
• Strong visual impairment (> 5 diopters) not corrected by contact lenses.

Exclusion criteria for acrophobic patients:

• Patients continuing psychotherapy.
• Patients suffering from other neurological disorders or comorbid psychiatric diseases than acrophobia.
• Patients suffering from severe organic disorders that could disable or disrupt the therapeutic process.
• The concomitant drugs at inclusion should not be modified or discontinued during the study.
• No psychotherapy should be initiated during the study.

Exclusion criteria for healthy volunteers:

- Subjects with a known psychiatric or neurological disorders, diagnosed for depression, with emotional disorders affecting their perception of the environment, or taking a medication that may affect the auditory and visual perception, concentration or emotions.