The interface of technology and medicine is creating exciting possibilities for psychiatry and the behavioral sciences. A particularly intriguing one is the marriage of virtual reality technology to established psychotherapeutic principles and techniques for the treatment of anxiety disorders.

Recent events such as the attacks on the World Trade Center and the Pentagon have posed unprecedented challenges for the provision of mental health services, most notably for the treatment of posttraumatic stress disorder (PTSD). Expert treatment guidelines published in 1999 proposed imaginal exposure therapy as the standard of care for PTSD (1). Although at least 12 controlled clinical trials have documented the efficacy of this form of therapy, treatment failures remain a notable problem.

Imaginal exposure presents an impossible dilemma for some patients. Its effective use requires that a patient repeatedly recount his or her traumatic experience in the present tense to the therapist. However, avoidance of reminders of the trauma is a symptom of PTSD. Thus some patients refuse to undertake this treatment, and although some others are willing, they are unable to engage their emotions or senses. They retell the story in a flat emotionless manner that reflects their numbness, and their PTSD symptoms do not improve. The few studies that have addressed the question of treatment failures have concluded that failure of the patient to engage emotionally predicts a poor treatment outcome (2).

Exposure-based therapy for PTSD using virtual reality technology was introduced by Rothbaum and her associates (3), who based their work on the theories of Foa and Kozak (4). Rothbaum and coworkers (3) were the first to propose that the illusion of presence in the virtual world facilitates emotional processing of memories associated with the traumatic event.

For exposure therapy using virtual reality technology, the patient wears headgear shaped like a helmet that contains two built-in, goggle-sized miniature computer monitors that are positioned close to the patient's eyes. Position tracking devices built into the helmet keep the computer informed of changes in the user's head location. The movements of the user's head cue the tracking device to project changing images. For example, virtual objects in front of the user become closer as the user leans forward. Thus the user is given a uniquely compelling experience of existing in the virtual world—a highly realistic, three-dimensional, computer-simulated environment.

Until now, psychotherapy in general and imaginal exposure in particular have relied on the capacities of a patient's imagination and memory. However, virtual environments afford opportunities not only to capitalize on a patient's capacities (5) but also to augment them with visual, auditory, and even haptic computer-generated experiences (6).

Virtual reality affords both the clinician and the patient several advantages over other types of exposure therapy. For patients who are reluctant to engage in recollections of feared memories, virtual reality provides a sensory-rich and evocative therapeutic environment that allows patients to experience a "sense of presence" in the virtual environment (7). An important feature of this technology is that it allows for graded exposure to increasingly feared environments, which can be carefully monitored and tailored to the individual patient's needs (8). Virtual environments can be manipulated above and beyond the constraints of the everyday world, thus creating new possibilities for therapeutic action (9). As a result, therapy that uses this technology can increase patients' feelings of self-efficacy and of being active agents of their own experience. Also, patients have been found to be more willing to agree to exposure therapy that involves virtual reality than other forms of exposure therapy. Entering the virtual world usually does not involve the same risks as returning to the feared environment. In addition, patients feel supported knowing that the therapist is also viewing the virtual environment and sharing their experiences.

Thus, for patients with PTSD who are fearful of recounting their experiences—or unable to do so—virtual reality technologies offer an external setting in which they can encounter their trauma and master its effects. Because of the multiplicity of sensory cues that virtual reality affords, patients may become more involved in their treatment. In addition, this approach may facilitate processing of the traumatic experience. Because patients encounter the virtual environment at their own pace, a firm distinction is created between remembering and reliving (10).

Several case reports and controlled research studies attest to the utility of exposure therapy using virtual reality in the treatment of anxiety disorders, including acrophobia (11), fear of flying (12), arachnophobia (13,14), clau-strophobia (15), and PTSD (16). In two instances, graded exposure using virtual reality has been used successfully to treat combat-related PTSD. In a case reported by Rothbaum and colleagues (15), a man who had served in Vietnam 26 years earlier underwent a 14-session virtual reality treatment. He suffered from chronic PTSD and major depression and had a history of substance abuse. During the initial session, the therapist described the treatment and the patient was given an opportunity to familiarize himself with the equipment. Over subsequent sessions, held twice-weekly, he viewed two virtual reality environments: a jungle scene accompanied by sound effects such as crickets, gunfire, helicopters, mine explosions, and men shouting "Move out!" and a Huey helicopter in which the backs of the pilots' heads were visible, as well as the view of the ground from the helicopter's side door.

The therapist encouraged the patient to engage with the scenes until he was habituated to them. The investigators reported that during the fourth and fifth sessions, the patient recalled new memories, which he was asked to recount several times to allow for habituation. During the remaining sessions, the patient recounted other memories of his experiences in Vietnam, and the therapist matched these memories with scenes and sounds from the virtual environment. At the end of treatment, the therapist's rating of the severity of the patient's PTSD symptoms dropped by 34 percent—from the severe to the moderate range—and the patient's self-reported symptom levels decreased by 45 percent. These gains were maintained at six-month follow-up.

The effectiveness of virtual reality treatment for PTSD was further supported by Rothbaum and colleagues' study (3) of ten Vietnam veterans, which used the same treatment paradigm. The severity of all patients' symptoms decreased, and the declines ranged from 15 percent to 67 percent at six-month follow up.

These successes, coupled with studies examining the utility of virtual reality exposure therapy in treating specific phobias, provide compelling grounds for further developing this technology to treat chronic PTSD. Two of the authors (JD and HH) are currently studying the efficacy of virtual reality exposure therapy in the treatment of patients who have PTSD as a result of trauma they experienced during the attacks on the World Trade Center. This new treatment program offers graduated exposure to the attacks. After several graduated sessions, patients are able to experience the most realistic version of the virtual environment in which a jet collides with a building and the building collapses after an explosion. The program gives severely traumatized patients the opportunity to gradually and systematically approach multiple feared situations associated with the World Trade Center attacks, including fears of flying, heights, and elevators, in addition to the traumatic event itself.

This marriage of antithetical traditions, the antitechnology of verbal therapies with the most modern of inventions, may come to play a significant role in systematizing treatment of PTSD after community disasters, such as terrorist attacks, and natural disasters, which are often experienced by large numbers of people. Although each individual's experience is unique, common elements might in some cases be scripted, allowing for delivery of effective treatment to many effected people and suggesting the possibility of developing a treatment technology for psychotherapy.

Dr. Difede and Dr. Jaysinghe are affiliated with the department of psychiatry at Weill Medical College of Cornell University, 525 E. 68th Street, Box 200, New York, New York 10021 (e-mail, jdifede@med.cornell.edu). Dr. Hoffman is with the Human Interface Technology Laboratory at the University of Washington in Seattle. Ian E. Alger, M.D., is editor of this column.