TO THE EDITOR
Virtual reality technology and pain relief
The potential of virtual reality (VR) technology to mitigate the discomfort and distress associated with invasive medical procedures is being explored[1]. Although the precise mechanism by which VR technology exerts its analgesic effects remains unclear, patients' VR experience has been observed to modulate functional brain networks, thereby contributing to pain relief and the attenuation of pain-related anxiety[2]. During the experience of pain, the salience network (SN), a functional network comprising the anterior cingulate cortex and insular cortex, is activated. Anxiety is increased when the SN functionally connects with the hippocampus and amygdala. Conversely, the default mode network (DMN), a functional network of the medial prefrontal cortex (mPFC), posterior cingulate cortex, precuneus, and inferior parietal lobe, represents a neural activity that enables the brain to disengage from independent thought, information processing, and judgment. A shift in brain network activity from the SN to the DMN through VR technology has been demonstrated to result in pain suppression[3]. Nevertheless, there are instances wherein VR technology proves to be ineffectual in alleviating pain, necessitating an investigation into the underlying causes. In this article, we will examine two issues pertaining to the alleviation of pain through the use of VR technology. One issue is whether the technology is immersive or non-immersive. The other issue pertains to the discrepancy in the efficacy of VR technology in alleviating chronic vs acute pain.
Immersive vs Non-immersive VR
VR technology has experienced significant advancements, with its potential applications becoming increasingly diverse. As the concept of VR continues to evolve, a significant challenge emerges: The lack of unified research methods and standards for evaluating the efficacy of pain relief using VR. Although it is an application of VR technology, the stimulation provided to the brain by the device is also markedly distinct. VR technology can be broadly classified into two categories: Immersive and non-immersive.
VR experiences have been demonstrated to stimulate the brain, activating neural pathways that are typically challenging to engage and modifying the functional connectivity of the brain[2]. If an experience utilizing VR technology is successful in transitioning the brain network from the SN during pain to the DMN, which is more aligned with the initial state, pain relief will ensue. Immersive types necessitate the use of additional equipment and are more costly, yet they provide a more pronounced stimulation effect on the brain circuitry than non-immersive types[4,5]. Furthermore, they facilitate the induction of the DMN in the brain network with greater ease. Non-immersive types are relatively simple devices and may be readily introduced, but real-world stimuli are always likely to enter the brain. In non-immersive environments, it is challenging to eliminate real-world stimuli, which hinders the creation of an immersive VR experience. Consequently, the capacity to prompt a shift in the brain's functional connections is limited. The distinction between immersive and non-immersive stimuli hinges on the degree of stimulation to the body's senses. When the DMN becomes significant through bodily illusion, there is a reduction in pain perception by the SN. Given that the degree of bodily illusion is more pronounced in immersive environments, the pain reduction effect is greater than in non-immersive environments. The use of immersive VR technology enables users to become completely immersed in a virtual space, effectively disconnecting them from the real world. Wearing a head-mounted display (HMD), the user establishes a connection to the virtual world through the use of sight, sound, and, in some cases, touch. It is anticipated that this approach will prove more efficacious than non-immersive techniques in suppressing pain perception, due to its capacity to divert attention away from pain-related thoughts and immersing the user in a virtual environment. The high level of immersion afforded by immersive VR has been demonstrated to be an effective method for alleviating brief periods of intense pain, such as that experienced during medical procedures.
Conversely, one of the disadvantages of immersive environments is simulator sickness[6]. Simulator sickness during VR is a phenomenon that presents symptoms analogous to those observed in motion sickness, including dizziness, nausea, and headaches, which manifest when an individual is engaged in a VR experience. In a VR environment, visual information is in motion, yet the body remains stationary. To obviate this phenomenon, it is recommended to commence with brief periods of exposure and subsequently extend the duration of the VR experience. This phenomenon can be mitigated by modifying the viewing angle and frame rate within the VR device settings[7].
Moreover, the impact of VR technology is contingent upon the specific program and application utilized. A significant number of VR programs incorporate guided meditation and relaxation exercises[8]. There are several methods in place to combine VR and mindfulness[9]. Recreating natural environments with a relaxing effect, such as the seaside, forests, and grasslands, in VR. Introducing a simple environment into the VR space that allows you to concentrate on meditation. Visualizing your own body through an avatar and focusing on physical sensations. Performing autogenic training in the VR space using guided audio from an expert. Expressing breathing techniques and relaxing each part of the body with visual effects. These are combined with interactive elements that change the VR space in sync with the user's heart rate and breathing. These combine visual and auditory elements with the objective of promoting mindfulness and stress reduction, as well as reducing pain perception. Some VR applications employ biofeedback mechanisms to assist users in comprehending their physiological response to pain. The real-time visualization of heart rate and muscle tension facilitates the acquisition of relaxation techniques and an enhanced capacity to manage pain.
Consequently, when examining VR research papers, it is essential to consider the potential variability in the impact of brain network switching, which may be influenced by several factors, including the type of device utilized, the nature of the stimuli presented, the specific program employed at the time, and the application used in conjunction with it.
Differences in effectiveness between acute and chronic pain
It has been demonstrated that the use of VR technology as a distraction is an effective method for reducing acute pain. VR technology has been employed to alleviate the discomfort and apprehension commonly associated with the administration of anesthesia[10]. Furthermore, the analgesic impact of VR during burn treatment and the suturing of traumatic injuries has been corroborated[11]. Acute pain arises when a physical stimulus is transmitted ascendingly to the primary somatosensory cortex. The phenomenon of acute pain relief by distraction is achieved by inhibiting this ascending pain transmission system (lateral pain system), whereby pain stimuli sensed by nociceptors are transmitted to the primary somatosensory cortex via the spinal cord and thalamus. When the lateral pain system is activated, the brain activates the SN, which detects that an anomalous event has occurred. In contrast, experiences involving VR have been observed to activate the DMN while simultaneously reducing activity in the SN. The DMN strengthens the functional connectivity between the mPFC and the cerebellum, and activates the descending pain inhibitory pathway, which transmits inhibitory signals from the primary somatosensory cortex to the spinal cord via the aqueductal gray matter. Inputs such as visual stimulation by VR have been observed to inhibit the activation of this nervous system. Additionally, the shift of attention by VR has been shown to inhibit the transmission of information in the primary somatosensory cortex. Finally, acute pain can be alleviated by changes in pain-processing brain networks[12].
In contrast, chronic pain is associated with an altered brain network that processes pain, and it is challenging to fully reset this altered network through VR stimulation alone. VR is currently being investigated as a potential treatment for chronic pain for which no effective treatment has yet been established[13]. Some studies have demonstrated the efficacy of VR therapy for a range of chronic pain conditions with unknown etiologies, including fibromyalgia, neuropathic pain, and chronic low back pain. Nevertheless, the analgesic effect of VR is demonstrably more pronounced in the context of acute pain than in chronic pain[14]. Individuals with chronic pain exhibit altered patterns of DMN activity in comparison to healthy individuals. Firstly, in individuals experiencing chronic pain, the DMN is linked to the affective system and is associated with negative thoughts and feelings related to pain[15]. Therefore, a simple switch from the sensorimotor to the DMN is not as effective in chronic pain as it is in acute pain. In individuals experiencing chronic pain the functional connections of the mPFC in the DMN are observed to be weak, while those with the lateral prefrontal cortex, such as the superior frontal gyrus, are found to be strong[16]. In individuals with chronic pain, even when VR transitions from the SN to the DMN, the activity of the mPFC in the DMN remains weak, thereby impeding the formation of a connection between the DMN and the descending pain inhibitory pathway. The mPFC is a region of the brain that plays a central role in the DMN. The function of the mPFC is of significant importance in the reduction of pain through the use of VR as a distraction[17]. The mPFC has a close relationship with the basal ganglia and plays a role in regulating dopamine secretion to the basal ganglia. The direct projections from the mPFC to the basal ganglia are primarily directed to the striatum, which constitutes a part of the basal ganglia[18]. Additionally, there is a pathway that transmits information from the mPFC to the basal ganglia via the thalamus. The basal ganglia are densely populated by dopamine-secreting neurons, which process information from the mPFC and regulate the activity of extensive brain networks. In functional magnetic resonance imaging studies of chronic pain, a reduction in gray matter density has been observed in the mPFC[19]. This suggests a potential morphological and functional decline in the mPFC in individuals with chronic pain. Dopamine in the basal ganglia exerts an inhibitory effect on pain via the reward system and opioid nervous pathways[20]. In individuals with chronic pain, there is a dysfunction of the dopaminergic system, which is associated with a decrease in neurons in the mPFC[20]. It is unlikely that pain improvement will occur as a result of distracting the brain network with VR, given that the mPFC is less active in the DMN.
As a future challenge, it is hypothesized that if the relaxing and distracting effects of VR technology are augmented with elements that stimulate the function of the dopaminergic reward system, it will prove more effective for chronic pain. It can thus be concluded that the direct activation of the dopaminergic neurons with VR will result in an increased effectiveness of VR in the treatment of chronic pain. This method involves using VR programs that stimulate the reward system and release dopamine. Novelty and reward system stimuli, defined as the provision of new experiences in VR that cannot be experienced in the real world, have been demonstrated to stimulate dopamine secretion. VR content that is rewarding, such as games and social interactions, has been demonstrated to activate the brain's reward system and stimulate dopamine secretion[21]. For these approaches to be effective, it is necessary that the experience be as immersive as possible, that the distinction between the virtual and the real worlds be as difficult to discern as possible, and that the likelihood of promoting dopamine secretion be as high as possible. In order to improve chronic pain, a future challenge will be to study the effects of VR stimulation that releases dopamine in the reward system.
