Virtual reality cybersickness and the headache patient
Qian Cece Chen, Andrew Fleming, Adam Lepkowsky, Samer Narouze · Pain Medicine · 2024
Although virtual reality (VR) is widely marketed for entertainment, there has been a growing interest in utilizing it for pain therapy. VR immerses a patient in a computer-generated world. The deeper the immersion, the greater the distraction, which can lead to decreased processing of pain. Using VR is not without side effects as studies have shown that between 22 and 78% of users have experienced some form of side effects including cybersickness.1 As a result, headache patients, who are susceptible, have commonly avoided its usage. In a search for a solution to this problem, a recent study by Venkatakrishnan et al. showed that embedding a VR program with intermittent visual, auditory, or cognitive tasks could reduce the development of cybersickness.2 Although this distraction method may offer a possible way to mitigate cybersickness, for treatment use, any distraction away from the VR treatment program itself may reduce its effectiveness. Consequently, alternative methods for managing cybersickness are needed. Cybersickness is characterized by nausea, vomiting, headache, dizziness, eyestrain, prolonged sensory disorientation, and/or fatigue after exposure to VR.3,4 A study by Kim et al. aimed to elucidate risk factors for cybersickness found that smoking appeared to be protective, whereas a high Positive and Negative Affect Schedule (PANAS), a numerical scale used to determine a patient’s degree of positive or negative affect or emotions, appeared to be a risk factor for cybersickness.1 This study used a multivariable linear regression analysis to determine cybersickness risk based on age, sex, smoking, alcohol use, and various ophthalmological and ontological parameters. As evaluated by a Simulator Sickness Questionnaire (SSQ), used to assess and measure the level of cybersickness, their analysis showed no statistically significant increase or decrease in cybersickness risk for any of these groups aside from smoking and high PANAS as aforementioned.1 While VR software has rapidly improved in recent years, 2 programming variables have emerged as potential risk factors for causing cybersickness: virtual image scale factor and image delay time. Virtual image scale factor is a measure of the user’s field of view. A scale factor of 1.0, also known as neutral condition, provides the user with a field of view similar to viewing a computer screen, in which the user has minimal peripheral vision but still has a field of view otherwise similar to reality. Minification, with a scale factor of 0.5, or magnification, with a scale factor of 2.0, refers to a truncated field of view or a widened field of view, respectively. Image delay refers to delay in processing time between input and output that can cause, for example, motion in a scene to lag behind head movement. Draper et al. demonstrated a statistically significant increase in cybersickness with either minification or magnification, an effect that can last as long as 20 min postexposure.5 This study, as well as a study by Moss et al., demonstrated no significant difference in cybersickness between users who experienced image lag times.4 As these parameters continue to become more sophisticated and refined with advanced VR software, further research would be prudent to understand what parameters should be adjusted to minimize their effects on cybersickness. Cybersickness is believed to be due to a sensory mismatch between VR input and the vestibular system. It has been theorized that reducing this mismatch can have a preventative and therapeutic effect on those experiencing cybersickness. One approach involves using a motion platform that moves the body of the user along with virtually simulated motion. Pettijohn et al. studied participants in VR with no motion, VR with synchronous motion, or VR with asynchronous motion, and they were then evaluated using a SSQ. An ANOVA demonstrated no statistically significant difference among the groups with regard to incidence of cybersickness.6 Although more research should be conducted, these findings suggest that alternative methods may be more useful in practice. Direct stimulation of the vestibular system has emerged as another proposed therapeutic method to reduce cybersickness. A study by Groth et al. focused on galvanic vestibular stimulation (GVS). To reduce cybersickness, the authors employed low-current electrical stimulation of participants’ vestibular canals correlated with the degree of motion perceived by the user during VR. Evaluation of participants’ SSQ revealed that cybersickness was reduced by GVS.3 As a novel therapy, GVS in tandem with VR would also benefit from further research but appears to show great potential. To delve further into the neuroscientific basis for using GVS, Ahn et al. studied the neural pathway that may be implicated in cybersickness by examining the interplay between visual and vestibular networks in VR. The vestibular end-organs in the inner ear play a crucial role in detecting linear and angular acceleration. Visual perception contributes to one’s perception of self-motion. Participants were subjected to either accelerating or linear movement via VR and classified as cybersickness susceptible (CS) or non-susceptible (CNS) based on their SSQ scores. While in VR, participants were examined using EEG. Findings revealed significant inhibitory signaling in the parieto-insular vestibular cortex (PIVC) during visual stimulation. The CS group exhibited a higher alpha wave power spectral density compared to the CNS group for both types of VR motion.7 These findings suggest that cybersickness originates from a visual-vestibular mismatch influenced by individual neurological connectivity that may vary between susceptible and non-susceptible populations. Therefore, targeting the vestibular system may result in effective treatments. Currently, there are two methods proposed to treat cybersickness via stimulating the vestibular system—GVS and bone-conducted vibration (BCV). While GVS uses direct stimulation, BCV uses indirect vibratory stimulation over the mastoid bone to reduce the cue mismatch. Patients who undergo GVS wear a headpiece that secures one electrode to bilateral mastoid bones. Small electrical currents are then transmitted through these electrodes in order to stimulate the vestibular nerve on either side of the patient’s head. In the setting of VR, these currents are coordinated with the VR program so that electrical stimuli correspond to visually perceived linear or angular acceleration in the VR screen. BCV is performed in a similar manner but uses superficial vibrations at each mastoid bone to stimulate the vestibular nerve. GVS has certain limitations (contraindicated in patients with pacemakers/ICDs) and has been shown to have variable success rates due to the risk of increasing cue mismatch if stimulation is uncoupled with whatever motion is presented by the VR setting. This is in contrast to BCV, which attempts to prevent cybersickness by adding noise to the vestibular input. Central processing of this vestibular input recognizes the noisy input as unreliable. By reducing the brain’s perceived reliability of vestibular input, BCV theoretically reduces the dissonance between the visual input from their VR program and their vestibular input, theoretically reducing cybersickness.8 In Weech’s study, there was a statistically significant decrease in SSQ scores for patients with BCV coupled to their VR angular movements as compared to controls.8 This provides evidence that BCV could be a viable means to decrease cybersickness in patients who would benefit from VR therapy. Despite the general avoidance of VR use in headache patients, some studies have illustrated potential a benefit of VR in treating chronic headache in both pediatric and adult patients. In a study by Tommaso et al., patients in VR simulations of either a standard hospital room or an idyllic setting were exposed to laser-evoked potentials (LEPs) and their pain scores were recorded. In the idyllic setting, chronic migraine patients had reduced pain and higher modulation of bilateral parietal cortical areas during painful stimulation with LEPs compared to control.9 In another study, Shiri et al. studied the effects of biofeedback with VR on pediatric chronic headache patients. Notably, this study sought to find an alternative means for treating chronic headaches given the low success rate of pharmacological therapy in this population. Ten pediatric chronic headache patients underwent biofeedback relaxation therapy while observing positive VR images of themselves. Nine out of ten patients reported improved pain ratings at both 1 and 3 months post-treatment.10 Both studies suggest that VR should be studied further in order to elucidate its potential benefit for chronic headache patients. VR therapy for chronic pain, is an exciting new modality that could provide pain physicians with a non-pharmacological tool that could revolutionize the way we think about pain treatments. In recent years, VR has been approved for treatment of chronic pain syndromes such as low back pain; however, its use in chronic headache still requires further investigation. Compared to established treatment modalities such as analgesics and interventional options, VR has very minimal associated side effects. Its main potential side effect, cybersickness, is one of the main reasons for its current limited use in headache patients despite a lack of established evidence regarding any predisposition that chronic headache patients might have to experience cybersickness. It would be prudent, therefore, to further research such methods as vestibular nerve stimulation in an effort to develop non-invasive techniques that could facilitate VR therapy for chronic pain and particularly headache patients. None to report. Conflicts of interest: Authors have none to report.