VR for Mental Health — Part 2: Anxiety disorders

Written by Caitlín Hastings

This is the second instalment of our multi-part literature review on applying Virtual Reality (VR) to mental health interventions:

1. An overview of VR mental health interventions
2. Anxiety disorders
3. Post-traumatic stress disorder and depression
4. Eating disorders
5. Substance use disorder

Introduction

Over the past few years, Animorph have been exploring ways of understanding how the cutting-edge capabilities of Extended Reality (XR) may help with addressing medical challenges. We have embarked on an investigation of evidence-based research and are pleased to share our findings with the public.

In this section, we describe our findings in VR and anxiety disorders. We begin with an outline of the key concepts of VR and anxiety and then examine the contribution of VR in relation to specific anxiety disorders.

VR in anxiety; key concepts

As mentioned in our previous instalment, the majority of research in the current literature is focussed on anxiety disorders. This demonstrates the advantage of VR in the recreation of believable ‘real-world’ scenarios and its potential for ecological validity (1). Due to this, we will focus this piece on anxiety and review the effectiveness of VR in eliciting realistic anxiety responses in treatment and assessment. As anxiety was ranked the ninth largest contributor to global disability by the Global Burden of Disease Study in 2015, (2) VR has a potentially significant contribution to make.

As discussed in the last instalment, a large proportion of studies have revolved around exposure therapy (VRET) as VR is ideally suited to it. The first VRET study was conducted in 1995 (3). This looked at VR and acrophobia and demonstrated that VR was successful in reducing fear of heights. Since then, VRET has repeatedly been shown to be effective with other specific phobias but also with many other anxiety disorders. A treatment course for VRET follows typical clinical practice, with VR in place of the usual in vivo or visualisation techniques. This is advantageous in patients who may find imagining scenarios difficult. In high quality VRET, this can also be tailored to the patient. For instance, with flying phobia, certain aspects can be focussed on, such as the cabin door shutting in agoraphobic patients or turbulence and storms in those afraid of the plane crashing (4). This has been further developed in some cases, through the combination of other interventions or medications. For example, the use of repetitive transcranial magnetic stimulation (rTMS) over the left prefrontal cortex in individuals with spider phobia which was followed by exposure to spiders in VR. The combination reduced activations in the left inferior frontal gyrus (IFG) during functional near-infrared spectroscopy, when elicited by emotionally-irrelevant words with an emotional Stroop test (5).

As will be shown, exposure therapy is an important intervention technique. Due to the nature of VR, VRET can be radically adapted to individuals, therapy groups, and even the therapist administering it. Exposure therapy can used in ways that would not be possible in real world context. We will now discuss the contribution of VR in relation to specific anxiety disorders.

Specific phobias

A phobia is defined as a marked and persistent fear cued by the presence or anticipation of specific objects or situations, followed by a desire to avoid these because of high levels of fear and discomfort (6). Examples include flying phobia, needle phobia, and phobias of animals and heights. This is a widely studied area in VR and VRET has been found to beeffective in addressing phobias, with VRET having a lower drop-out rate than in vivo exposure therapy (7). Patients are more willing to cooperate as they are not as afraid to confront virtual phobias and maintain a feeling of control over the situation (8).

A meta-analysis which focussed on the efficacy of VRET in heights and fear of spiders found that VRET patients scored significantly better on behavioural assessment than those on inactive conditions (9). They also found no significant difference in behavioural assessment scores between VRET and standard behaviour therapy. A systematic review and quantitative meta-analysis which compared VRET to gold standard in vivo therapy found that there was a negative effect size in favour of in vivo exposure. However, this was non-significant and below the level of a small effect. This indicates that VRET is not significantly less efficacious than in vivo therapy (10). As VR technology improves, it may reduce the difference and even supersede in vivo with regards to certain phobias. At the very least, VR could provide a stepping stone to in vivo exposure. Effects from VRET also appear to be long-lasting, with research showing that these can persist from 3 months to 3 years. (11, 12, 13) Although, it must be noted, all of these studies are small and require repetition.

It has been suggested that the next steps in VRET research could investigate the optimal way to present stimuli. It has been shown that small changes to the context of presentation and using multiple stimuli can have an impact. (14) With these promising results, there is still work to be done to fine tune the process further.

Social anxiety disorder

Social anxiety disorder (SAD) is a condition marked by anxiety in social conditions which may involve judgement or evaluation by others and a consistent fear of embarrassment or humiliation. These types of situations may be faced and ‘suffered’ through or avoided altogether (15). Commonly in VR, fear-inducing scenarios are recreated, such as: classrooms, pubs or auditoriums — in the case of public speaking phobia (which we will discuss later in this instalment). Such environments are then populated with avatars which may react to the individual. While there is less research in social phobia and VR than specific phobias, perhaps due to the skill required to develop realistic environments and reactions from avatars, the results do appear to be encouraging.

Many studies focus on the feedback that individuals receive from VR avatars, as reported by Kishimito & Ding (16). This study also shows how effectively VR can elicit feelings of social anxiety for individuals with SAD. Participants with SAD and controls gave two 3-minute speeches and the effects of either ambiguous or negative virtual social feedback were examined. Individuals with SAD experienced higher levels of subjective anxiety when the feedback was ambiguous, and this was also higher than the controls. This also highlights the necessity for VR avatars to clearly manifest their emotions in SAD research. Likewise, a study by Lange & Pauli, where avoidance behaviour in individuals with SAD was studied, found that the facial expressions of avatars (neutral or angry) changed avoidance behaviour in participants when passing them. Participants with SAD had increased avoidance of both categories of avatar (17). As well as eliciting feelings of social anxiety, there are physiological markers connected to SAD that manifest when participants have undergone VR testing. Salivary cortisol, cardiovascular activity, electrodermal activity, eye movements, galvanic skin response and skin temperature have all been studied and found to be similar to those elicited in vivo experiences (18, 19, 20, 21).

Research has also shown that VR can have an impact as an intervention for SAD, with Morina et al. examining verbal interaction between individuals with SAD and avatars (22). This involved participants with high SAD having two sessions of free speech dialogue with avatars in anxiety-provoking situations while being monitored by a therapist. The results demonstrated significantly lower levels of social anxiety and high self-efficacy three months after exposure. A review conducted by Emmelkamp et al. found that there were no differences in efficacy between CBT and VRET in social phobia (23). However, there is a need to investigate VRET as a stand-alone treatment, as many randomised controlled trials (RCTs) have been conducted involving a combination of cognitive interventions and VRET.

VR also has the potential to be used as an assessment tool for SAD, but studies so far have been inconclusive. Kampmann et al. examined if a VR Behavioural Assessment Task (BAT) predicted social anxiety in daily life (24). They used two situations: one representing fear of small talk (engaging in conversation at a bus stop), and another representing fear of public speaking (attending a foreign language class where the teacher asked questions). Healthy participants were asked to rate anxiety with the subjective unit of distress scale (SUD). They were also asked to give an unrehearsed five-minute speech in front of a camera with a researcher present and then record their anxiety on the SUDs (in vivo BAT). It was shown that the individuals with high SUDs during the VR BAT reported higher social anxiety on a daily event survey, compared with the in vivo BAT which was found not to be a significant predictor of social anxiety as assessed by the State Social Anxiety Questionnaire.

In future research, there is a definite need for more studies which look at the interaction between individuals and avatars, especially verbally. These interactions should aim to be more natural and more unpredictable in order to allow individuals with SAD to challenge their beliefs. As examined in the next section, a lot of social anxiety research to date has been focussed more on performance or public speaking phobia as it is easier to programme a large auditorium space with a crowd, than a one-on-one experience.

Public speaking phobia

Public speaking phobia (PSP) is a sub-type of social anxiety and is a ‘performance’ related phobia rather than the more generalised social anxiety. This involves debilitating anxiety when speaking in front of crowds (25). It can have a long-term impact on academic, career, and social aspects of a sufferer’s life. It is one of the most common lifetime phobias (21.2%) (26), with sufferers overestimating negative judgement in others and underestimating their own ability. CBT and graduated exposure therapy have been found to be very effective in treatment. However, this requires the use of venues and an audience for an individual to practise, which is difficult to organise and not always economically viable. As avoidance is also a large part of PSP it can also be very difficult for patients to commence with this kind of therapy and there can be high drop-out rates (27).

Most studies have used a graduated exposure therapy and are based around common in vivo techniques; recreating feared situations such as classrooms and auditoriums and then manipulating a variable such as the audience size or their reactions to the speaker. This has also been found to affect real world behaviour, with follow-ups showing that these effects can be long-lasting. Anderson et al. compared in vivo therapy with VRET in a sample of 97 participants (28), where they were randomised to receive eight sessions of VRET, group exposure therapy or waiting list. It was found that both therapy groups had significantly improved from waitlist and this was maintained at 12 months. A follow-up study was conducted with the same group 4–6 years later and found that these effects were still evident for the VRET and in vivo exposure groups Anderson et al. (29). These findings have also been replicated in other studies and VRET has been shown to be a very viable alternative to in vivo therapy, removing many of the impediments to success such as cost and accessibility. There is a need to have more studies conducted with younger participants however, as this is a phobia which begins to affect individuals’ lives and academic performance from an early age (30).

To find out more on work which Animorph has conducted around public speaking phobia please visit our website.

Panic disorder and agoraphobia

Panic disorder and agoraphobia have been combined here for ease, but while these conditions frequently occur together they may also arise individually with no history of the other. Panic disorder is classified as a sudden rush of anxiety symptoms (palpitations, sweating, digestive discomfort, derealisation, fear of dying, going crazy etc.) which tend to peak within 10 minutes of onset. In the case of panic disorder with agoraphobia (PDA), these anxiety symptoms are provoked by situations where an individual may feel they cannot escape, where escape may be embarrassing, or help may not be available. These situations tend to take place outside of the home where an individual would be on their own such as on public transport, being in crowds or standing in a line or on a bridge. This has the effect that individuals will avoid these situations or will endure them with distress or only with a companion (31).

As with other forms of VRET, situations which elicit anxiety are presented to individuals (e.g. a cinema, tunnel, crowded bus) and a graduated procedure is followed. If efficacious, this is preferable to working outside the clinical environment as it is more confidential, secure and controlled for both the patient and therapist. There is not a large amount of research on VR and PDA but the majority of studies which have been carried out have had positive results, finding VR comparable to conventional treatment or more successful in some cases (32, 33). It also appears to have an earlier impact and shows good results at follow-up (34, 35). However, despite this earlier effect on symptoms, the long-term outcome is similar to the standard treatment CBT. Future research could aim to harness this advantage to create a more economical and less stressful therapy method for patients.

Generalised anxiety disorder

Generalised anxiety disorder (GAD) is a condition where patients experience daily, persistent, intrusive and excessive worrying about a range of topics, from which they are unable to distract themselves. This can interfere with daily life, affect concentration, and cause irritability, restlessness, fatigue and muscle tension (36). It is one of the most common disorders noted in primary care, and it is estimated that two-thirds of the patients suffering from GAD do not receive anytreatment for it. Complete remission after 5 years of clinical treatment occurs in only 18–35% of patients and it is associated with other disorders such as depression (37).

The first study to look at GAD and VR (38) investigated relaxation techniques where VR was combined with biofeedback. The small sample size meant that between-group analyses were not possible. In the experimental conditions VR had an impact in reducing symptoms of GAD with biofeedback contributing to this. The physiological effects of VR on anxiety were also shown in a study, which combined VR with electroencephalogram (EEG) (39). The control condition (quiet rest) and VR-assisted meditation significantly reduced subjective reports of anxiety and increased Alpha power. (Increased alpha power has been associated with mindfulness in other studies also (40). However, only the VR intervention resulted in lower Beta frequencies, and significantly reduced broadband Beta activity in the anterior cingulate cortex, which is in keeping with research showing a physiological reduction in anxiety. (Beta waves tend to be observed in a wakened state and are associated with logical thinking and have a stimulating effect (41). These findings are promising and demonstrate that VR could have an impact on this disorder. However, outside of this study, there have not been many similar trials. A review by Maples-Keller et al. proposed that this lack of studies may be a result of the myriad worries that individuals with GAD experience and suggested that future research could focus on common subtypes such as health anxiety, finances, or relationships (42).

With this observation in mind, general treatments such as simple relaxation and mindfulness techniques should could be further investigated as they could be helpful for most individuals. A recent study by Navarro-Haro et al. investigating mindfulness in GAD with VR (43). Poor concentration in GAD can greatly impact therapy as patients may find it hard to follow. This is where VR may have an advantage, as patients can block out external distractors more easily and are presented with visual and auditory stimuli. The study took advantage of the ‘immersive’ qualities of VR, which allow the patients to be present in a computer-generated world. Mindfulness training was found to reduce anxiety in the group that was receiving additional VR and those receiving mindfulness alone. The training also effected symptoms in depression, emotional regulation and interoceptive awareness. Patients with the additional VR treatment were found to be significantly more adherent to the treatment (100% completion rate in mindfulness + VR vs. 70% completion rate in mindfulness alone); which may demonstrate that VR could prevent drop-out in this patient group. With the popularity of apps such as Headspace, there is a potential to expand this further in VR.

Obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a condition marked by intrusive, unwanted thoughts and ideas, which can be distressing (obsessions), and intentional, repetitive behaviour which can relieve anxiety (compulsions). Examples of common obsessions are contamination and a need for symmetry, and common compulsions are washing, counting and arranging objects in a certain manner (44). Currently, the most common therapy is CBT with exposure and response prevention (ERP), which involves exposure to an obsession-provoking situation and then prevention of the usual compulsion which the patient has learned will alleviate the anxiety associated with their obsession. Thereby teaching the patient to tolerate their distress or cope in a way which will not fuel their symptom cycle. For example, touching something the patient believes to be contaminated and then not washing their hands (45). However, in recent years it has been posited that metacognitive training (a therapy style which helps patients consider their problematic thinking style) could be as effective (46).

VR has the usual advantage here as situations difficult to explore in therapy can be recreated, such as a contamination obsession around public toilets. It can also act as a stepping stone for patients until they are ready to confront something in real life. Finally, it avoids the issues with diagnoses made using a patient’s retrospective memory as it allows therapists to observe behaviour in real-time. However, as with GAD, patients’ obsessions and compulsions may be highly idiosyncratic and they can experience many simultaneously. Therefore, it can be difficult to tailor a programme to match each patient exactly or to create one applicable for many patients. Perhaps because of this, there has not been much research in VR and OCD, except some studies showing that VR can elicit anxiety in those with OCD. These studies also demonstrated that the level of anxiety was associated with the level of presence experienced by the patients (47, 48). However, a study by Kim et al. which showed that anxiety was much higher in patients with OCD than in controls, also showed that their decrease in anxiety was much larger than that in controls, suggesting that using ERP in VR is viable (49).

There has also been some research looking at the idea of developing a VR assessment (50). A game was devised which aimed to provoke compulsions in individuals with OCD. It was found that the number of performed compulsions in the game was significantly higher for patients than controls. The sample size was small but there is potential that this kind of environment could also be used for ERP treatment as well as assessment if the patients can experience compulsions and anxiety in a realistic manner. However, like other areas in VR, there is a still a need for a randomised controlled trial looking at VR interventions for OCD.

Conclusion

This second instalment of our literature review illustrated the capacity of VR as an intervention and assessment tool in anxiety disorders. We have discussed the symptomatology of each disorder and how VR can elicit or treat these. We have also outlined the work that is still needed in many of these disorders.

The next instalment will discuss post-traumatic stress disorder and depression.

References

1. Bell, I. H., Nicholas, J., Alvarez-Jimenez, M., Thompson, A., & Valmaggia, L. (2020, June 1). Virtual reality as a clinical tool in mental health research and practice. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7366939/

2. GBD 2015 Disease and Injury Incidence and Prevalence Collaborators. (2016, October 8). Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015. PubMed. https://pubmed.ncbi.nlm.nih.gov/27733282/

3. Rothbaum, B. O. (n.d.). Effectiveness of computer-generated (virtual reality) graded exposure in the treatment of acrophobia. PubMed. https://pubmed.ncbi.nlm.nih.gov/7694917/

4. Maples-Keller, J. L. (2017). The Use of Virtual Reality Technology in the Treatment of Anxiety and Other Psychiatric Disorders. PubMed. https://pubmed.ncbi.nlm.nih.gov/28475502/

5. Deppermann, S. (2016, July 1). Functional co-activation within the prefrontal cortex supports the maintenance of behavioural performance in fear-relevant situations before an iTBS modulated virtual reality challenge in participants with spider phobia. PubMed. https://pubmed.ncbi.nlm.nih.gov/26996315/

6. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

7. Freeman, D., Reeve, S., Robinson, A., Ehlers, A., Clark, D., Spanlang, B., & Slater, M. (2017, October 1). Virtual reality in the assessment, understanding, and treatment of mental health disorders. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5964457/

8. Garcia-Palacios, A. (2017, March 22). Comparing acceptance and refusal rates of virtual reality exposure vs. in vivo exposure by patients with specific phobias. PubMed. https://pubmed.ncbi.nlm.nih.gov/17927544/

9. Morina, N., Ijntema, H., Meyerbröker, K., & Emmelkamp, P. M. G. (2015, November 1).Can virtual reality exposure therapy gains be generalized to real-life? A meta-analysis of studies applying behavioral assessments. ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S0005796715300334?via%3Dihub

10. Wechsler, T. F., Kümpers, F., & Mühlberger, A. (2019, September 10). Inferiority or Even Superiority of Virtual Reality Exposure Therapy in Phobias? — A Systematic Review and Quantitative Meta-Analysis on Randomized Controlled Trials Specifically Comparing the Efficacy of Virtual Reality Exposure to Gold Standard in vivo Exposure in Agoraphobia, Specific Phobia, and Social Phobia. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6746888/

11. Kaussner, Y. (2020, January 7). Treating patients with driving phobia by virtual reality exposure therapy — a pilot study. PLoS ONE. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0226937

12. Mühlberger, A., Weik, A., Wiedemann, G., & Pauli, P. (2007, February 22). One-session virtual reality exposure treatment for fear of flying: 1-Year follow-up and graduation flight accompaniment effects. Taylor & Francis. https://www.tandfonline.com/doi/abs/10.1080/10503300500090944

13. Wiederhold, B. K., & Wiederhold, M. (2003, August 6). Three-year follow-up for virtual reality exposure for fear of flying. PubMed. https://pubmed.ncbi.nlm.nih.gov/14511458/

14. Shiban, Y., Schelhorn, I., Pauli, P., & Mühlberger, A. (2015, May 28). Effect of combined multiple contexts and multiple stimuli exposure in spider phobia: A randomized clinical trial in virtual reality. PubMed. https://pubmed.ncbi.nlm.nih.gov/26072451/

15. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

16. Kishimoto, T., & Ding, X. (2019, May 20). The influences of virtual social feedback on social anxiety disorders. PubMed. https://pubmed.ncbi.nlm.nih.gov/31106720/

17. Lange, B., & Pauli, P. (2019, December 23). Social anxiety changes the way we move — A social approach-avoidance task in a virtual reality CAVE system. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6927627/

18. Kothgassner, O., Felnhofer, A., Hlavacs, H., Beutl, L., Palme, R., Kryspin-Exner, I., & Glenk, L. (2016, September 1). Salivary cortisol and cardiovascular reactivity to a public speaking task in a virtual and real-life environment. ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S0747563216302400?via%3Dihub

19. Owens, M. E., & Beidel, D. C. (2014, September 5). Can Virtual Reality Effectively Elicit Distress Associated with Social Anxiety Disorder?Journal of Psychopathology and Behavioral Assessment. https://link.springer.com/article/10.1007/s10862-014-9454-x?error=cookies_not_supported&code=42bbaa2b-9a16-4746-bc32-0e2e6738ac4c

20. Dechant, M., Trimpl, S., Wolff, C., Mühlberger, A., & Shiban, Y. (2017, November 1). Potential of virtual reality as a diagnostic tool for social anxiety: A pilot study. ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S074756321730417X?via%3Dihub

21. Šalkevicius, J., Laukienė, I., Maskeliūnas, R., & Damaševičius, R. (2019, September 19). Anxiety Level Recognition for Virtual Reality Therapy System Using Physiological Signals. MDPI. https://www.mdpi.com/2079-9292/8/9/1039

22. Morina, N., Brinkman, W. P., Hartanto, D., Kampmann, I. L., & Emmelkamp, P. M. (2015). Social interactions in virtual reality exposure therapy: A proof-of-concept pilot study. PubMed. https://pubmed.ncbi.nlm.nih.gov/26410119/

23. Emmelkamp, A. M., Meyerbröker, K., & Morina, N. (2020, May 13). Virtual Reality Therapy in Social Anxiety Disorder. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7220867/

24. Kampmann, I. L. (2018, August 10). Self-report questionnaires, behavioral assessment tasks, and an implicit behavior measure: do they predict social anxiety in everyday life? PubMed. https://pubmed.ncbi.nlm.nih.gov/30128202/

25. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

26. Ruscio, A. (2007, November 2). Social fears and social phobia in the USA: results from the National Comorbidity Survey Replication | Psychological Medicine. Cambridge Core. https://www.cambridge.org/core/journals/psychological-medicine/article/abs/social-fears-and-social-phobia-in-the-usa-results-from-the-national-comorbidity-survey-replication/C2B4E1897DF043B6C076DCBDC417A2F0

27. Safir, M., Wallach, H., & Bar-Zvi, M. (2011, December 15). Virtual Reality Cognitive-Behavior Therapy for Public Speaking Anxiety: One-Year Follow-Up. Sage Journals. https://journals.sagepub.com/doi/10.1177/0145445511429999?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub++0pubmed&

28. Anderson, P. L., Price, M., Edwards, S. M., Obasaju, M. A., Schmertz, S. K., Zimand, E., & Calamaras, M. R. (2013). Virtual reality exposure therapy for social anxiety disorder: A randomized controlled trial. American Psychological Association. https://doi.apa.org/doiLanding?doi=10.1037/a0033559

29. Anderson, P. L., Edwards, S. M., & Goodnight, J. R. (2016, November 15). Virtual Reality and Exposure Group Therapy for Social Anxiety Disorder: Results from a 4–6 Year Follow-Up. Cognitive Therapy and Research. https://link.springer.com/article/10.1007/s10608-016-9820-y?error=cookies_not_supported&code=317c9e8d-cf11-4b82-9233-7f88955fce86

30. Kahlon, S., Lindner, P., & Nordgreen, P. (2019, December 27). Virtual reality exposure therapy for adolescents with fear of public speaking: a non-randomized feasibility and pilot study. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933883/

31. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

32. Pitti, C., Peñate, W., de la Fuente, J., Bethencourt, J., Acosta, L., Villaverde, M., & Gracia, R. (2008). [Agoraphobia: combined treatment and virtual reality. Preliminary results]. PubMed. https://pubmed.ncbi.nlm.nih.gov/18365789/

33. Malbos, E., Rapee, R. M., & Kavakli, M. (2012, July 11). A controlled study of agoraphobia and the independent effect of virtual reality exposure therapy. PubMed. https://pubmed.ncbi.nlm.nih.gov/22790176/

34. Vincelli, F., Anolli, L., Bouchard, S., Wiederhold, B. K., Zurloni, V., & Riva, G. (2003, June). Experiential cognitive therapy in the treatment of panic disorders with agoraphobia: a controlled study. PubMed. https://pubmed.ncbi.nlm.nih.gov/12855090/

35. Botella, C. (2007, May 1). Virtual reality exposure in the treatment of panic disorder and agoraphobia: A controlled study. Wiley Online Library. https://onlinelibrary.wiley.com/doi/abs/10.1002/cpp.524

36. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

37. Navarro-Haro, M., ALARCÓN, M., Hoffman, H., & Montoyo, A. (2019, January 28). Evaluation of a Mindfulness-Based Intervention With and Without Virtual Reality Dialectical Behavior Therapy® Mindfulness Skills Training for the Treatment of Generalized Anxiety Disorder in Primary Care: A Pilot Study. Frontiers. https://www.frontiersin.org/articles/10.3389/fpsyg.2019.00055/full

38. Pallavicini, F., Gorini, A., Algeri, D., Repetto, C., Gaggioli, A., & RivaPages39, G. (2010). IOS Press Ebooks — Virtual Reality in the Treatment of Generalized Anxiety Disorders. IOS Press Ebooks. http://ebooks.iospress.nl/publication/13020

39. Tarrant, J., Viczko, J., & Cope, H. (2018, July 24). Virtual Reality for Anxiety Reduction Demonstrated by Quantitative EEG: A Pilot Study. Frontiers. https://www.frontiersin.org/articles/10.3389/fpsyg.2018.01280/full

40. Lomas, T., Ivtzan, I., & Fu, C. H. (2015, October 9). A systematic review of the neurophysiology of mindfulness on EEG oscillations. PubMed. https://pubmed.ncbi.nlm.nih.gov/26441373/

41. Gawali, B., Abhang, P., & Mehrotra, S. (2016, January 1). Technical Aspects of Brain Rhythms and Speech Parameters. ScienceDirect. https://www.sciencedirect.com/science/article/pii/B9780128044902000038

42. Maples-Keller, J. L., Bunnell, B. E., Kim, S. J., & Rothbaum, B. O. (2017). The Use of Virtual Reality Technology in the Treatment of Anxiety and Other Psychiatric Disorders. PubMed. https://pubmed.ncbi.nlm.nih.gov/28475502/

43. Navarro-Haro, M., ALARCÓN, M., Hoffman, H., & Montoyo, A. (2019, January 28). Evaluation of a Mindfulness-Based Intervention With and Without Virtual Reality Dialectical Behavior Therapy® Mindfulness Skills Training for the Treatment of Generalized Anxiety Disorder in Primary Care: A Pilot Study. Frontiers. https://www.frontiersin.org/articles/10.3389/fpsyg.2019.00055/full

44. Psychiatry Online | DSM Library. (n.d.-d). Psychiatry Online. https://dsm.psychiatryonline.org/doi/book/10.1176/appi.books.9780890425596

45. Simpson, H. B., & Simpson, D. M. (2019, January 1). Exposure and response prevention for obsessive-compulsive disorder: A review and new directions. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6343408/

46. Philipp, R., Kriston, L., Lanio, J., Kühne, F., Härter, M., Moritz, S., & Meister, R. (2018, December 16). Effectiveness of metacognitive interventions for mental disorders in adults-A systematic review and meta-analysis (METACOG). PubMed. https://pubmed.ncbi.nlm.nih.gov/30456821/

47. Kim et al., (2008, December). Anxiety provocation and measurement using virtual reality in patients with obsessive-compulsive disorder. PubMed. https://pubmed.ncbi.nlm.nih.gov/18991527/

48. Laforest, et al., (2016, August 5). Inducing an Anxiety Response Using a Contaminated Virtual Environment: Validation of a Therapeutic Tool for Obsessive–Compulsive Disorder. Frontiers. https://www.frontiersin.org/articles/10.3389/fict.2016.00018/full

49. Kim et al., (2008, December). Anxiety provocation and measurement using virtual reality in patients with obsessive-compulsive disorder. PubMed. https://pubmed.ncbi.nlm.nih.gov/18991527/

50. Bennekom, et al., (2017, November 1). A Virtual Reality Game to Assess Obsessive-Compulsive Disorder. Liebertpub. https://www.liebertpub.com/doi/10.1089/cyber.2017.0107