The Neurobiology of Virtual Reality Pain Attenuation XXXXXX Neuropharmacology 4-9-08
Outline • What is Virtual Reality • Introduction • Virtual Reality as a Distraction
What is Virtual Reality • “a realistic simulation of an environment, including three-dimensional graphics, by a computer system using interactive software and hardware.“
Introduction • Has been shown to be a powerful clinical tool in a variety of applications. • Has been particularly effective when used to manage acute pain with patients undergoing invasive medical procedures. • Field of VR pain attenuation is still in its infancy.
Virtual Reality as a Distraction • Distraction is an effective means of managing pain during acute and invasive medical procedures. • VR distracts the patients from the unpleasantness of the procedure and hospital setting by putting them in a pleasant and absorbing virtual environment. • This is done through visual, auditory and tactile cues. • Use of VR helmets helps the patient to focus on the virtual environment by limiting visual and auditory stimuli from the outside world.
Experiments • Earliest study looked at the effects of visual input on phantom limb sensation(16) • Used a “virtual reality mirror box” • 6 out of 10 patients reported sensation in their phantom limb after viewing the mirror image of their uninjured hand. • Studies with burn victims (9,10,11,23) have shown that virtual environments can produce profound nonpharmacological analgesic effects, significantly reducing pain during physical therapy. • These effects occurred with VR therapy alone and when it was coupled with analgesic drugs. • Other studies have shown the benefits of virtual reality for outpatient chemotherapy for breast cancer, adolescents with cancer undergoing lumbar puncture, children undergoing venipuncture, and children requiring IV placement for MRI and CT scans. • Unfortunately, it is still not well understood how VR affects the perception of pain.
VR and the Neurobiology of Pain • Pain is an extremely important sense as it is critical for the survival of an individual, as well as species. • Early studies have shown that pain is a subjective phenomena that is actually only loosely related to a specific injury or bodily insult. (1) • Today we know a great deal more about the ways pain is transmitted and perceived, modulated by the brain, and affected by drugs than we did in the past.
The Neurobiology of Pain • Normally, pain is detected by nociceptors. They are located throughout the body in the skin, muscles, and organs. • They respond to stimuli indicating any potential damage to tissue and then relay the information toward the central nervous system via A-delta fiber and C fiber neurons • A-delta fibers transmit those pain signals that are perceived as sharp or burning. • These fibers are myelinated, with conduction speeds of up to 30m per second, to handle such important information. • C fibers deal with dull and aching pain signals. • These fibers are not myelinated, with conduction speeds of only 0.5-2m per second, due to the lower priority of such signals.
The Neurobiology of Pain • By interrupting the body’s normal means of detecting pain, analgesia can be achieved. • Primary target of analgesic development has been the C fibers. • It is unlikely that analgesia produced by VR is due to direct effects on C fiber signaling. • Gate Control Theory (GTC) says that “nerve gates” determine the degree to which a pain sensation enters into the awareness of an individual. • On top of GTC the existence of an intricate descending pain-control system that originates in the brain has been demonstrated. • Activation of this system occurs through the fibers descending from the periaqueductal grey (PAG) area of the midbrain. • This activation produces pronounced analgesia. • Microinjections of opioid agonists into the this system have also produced analgesia. • Electrical stimulation of the PAG has produced analgesia. • Opioid agonists, such as naloxone, have blocked such analgesia. • This system can also facilitate the transmission of pain. • Possibly explains why the experience of heightened pain is often produced by hypervigilance and emotional concerns about pain. • The PAG also receives input from various areas of the brain, including those cortical regions involved in attention and emotion. • This suggests that the modulation of the descending pain-control system might underlie the effects of emotion and attention on the perception of pain.
Attention, VR, and Pain • VR works by distraction • fMRI studies have shown that cortical areas associated with attentional processes and pain modulation are more active during distraction, while those areas associated with pain perception are less active. • During pain with distraction compared to pain alone, he PAG, orbitofrontal cortex, and perigenual ACC all show increased activation. • Areas of the pain matrix showing decreased activation during distraction include the insular cortex, midcingulate ACC and the thalamus.
Attention, VR, and Pain • The ACC is divided into two sections 1. Perigenual • Functions to mediate the attentional processes and emotional reaction to pain. • Shows increased activity during distraction to pain. • Activation produces analgesia. 2. Midcingulate • Demanding cognitive tasks activate it. • Shows decreased activity during distraction to pain. • Given that the descending pain-modulation pathway can be activated by stimulation of the PAG, it is hypothesized that the ACC effects structures, such as the PAG, that modulate pain. • The VR distracts the person activating the perigenual ACC activating the PAG stimulating the descending pain-modulation system producing analgesia.
Emotion, VR, and Pain • Emotion can also have an impact on the perception of pain. • Thought to occur via the descending pain-control system. • The amygdala can produce either inhibition or facilitation of pain perception by interacting with the ACC and the PAG • There is evidence showing that negative emotions, such as fear and stress, activate a section of the amygdala, which results in the inhibitory pain-control pathways being activated. • Other evidence shows that negative emotions like anxiety and depression, result in the facilitation of pain. • One study has shown than positive emotions can result in a decrease in pain. • This analgesia is theorized to occur due to the emotions inhibiting the portion of the amygdala that facilitates pain. • Greater research is needed in this area though to fully understand the mechanisms of action though.
Conclusion • Despite all the studies showing the efficacy of using VR, we still do not know all the neurobiological mechanisms underlying it. • Further research targeting the neurobiological correlates of pain attenuation are needed. • This is necessary so that we might better understand the biological and psychological factors that govern pain. • Future research could lead to the development of new and more effective methods of using VR to treat pain.
Sources • Gold, J., Belmont, K., & Thomas, D. (2007, August). The Neurobiology of Virtual Reality Pain Attenuation. CyberPsychology & Behavior, 10(4), 536-544.