Woolf conducted his own experiment in Wall’s lab, applying painful stimuli to the hind legs of rats. The animals developed large “fields” of pain that could be easily activated months later with a light tap or gentle heat, even in areas not directly touched. “I was changing the function of the nervous system so that its properties changed,” Woolf says. “Pain was not just a measure of some peripheral pathology,” he concluded; it “may also be due to abnormal reinforcement in the nervous system – this was the phenomenon of central sensitization.” Before this discovery, he says, “the feeling has always been that pain is a symptom that reflects a disease, and now we know that pain is often a result of a disease state of the nervous system itself.” Some conditions, such as rheumatoid arthritis, may present peripheral pathology as well as central sensitization. Others, such as fibromyalgia, characterized by pain throughout the body, are considered a problem of the central nervous system itself only.
Since Woolf’s experiment, there has been a greater understanding of how chronic pain changes the central nervous system. A.Vania Apkarian’s pain lab at Northwestern University found that when back pain persists, activity in the brain shifts from the sensory and motor areas to the areas associated with emotion, including the amygdala and hippocampus. “It’s part of internal psychology now,” Apkarian says, “a negative emotional cloud taking hold.”
The brain itself changes. Patients with chronic pain may show significant loss of gray matter in the prefrontal cortex, the brain’s attention and decision-making area that sits behind our foreheads, as well as in the thalamus, which relays sensory signals; both areas are important in processing pain. Excitatory neurotransmitters increase and inhibitory ones decrease, while glial and other immune cells cause inflammation; nervous system, unbalanced, magnifies and prolongs the pain. The system becomes confused, like an alarm that continues to sound even when there is no threat, even when the pain is no longer protective. Instead, it just causes more pain — and the longer it lasts, the more deeply systemic it gets and the harder it is to resolve.
There is a popular saying in neuroscience that when neurons fire together, they begin to connect together, an example of neuroplasticity in action. But if our brains are really plastic, what’s formed there can be reshaped. Therapies that target the brain rather than the aching back or knee — be it psychology, drugs, direct brain stimulation or virtual reality — could theoretically undo chronic pain.
In the 1990s, Hunter Hoffman, a cognitive psychologist at the University of Washington, began using VR to provide relief to burn patients who had to change their dressings — an excruciating ordeal that is difficult to treat. “Nobody used virtual reality to reduce patient pain for us,” he says. In his VR program called SnowWorld, patients who tumbled through the winter scene and threw snowballs at penguins reported that their relief was comparable to that of intravenous opioids. Brain scans confirmed these findings: VR and opioids each resulted in a marked reduction in neural activity in pain-related areas.
Unlike most drugs and surgical procedures, VR has far fewer side effects – mostly nausea and motion sickness. Headsets now cost a fraction of what they once did, and the graphics have been significantly improved, resulting in more immersive experiences and fewer potential side effects. In addition, Hoffman says, “all the major computer companies are pumping billions of dollars into virtual reality as a kind of internet” — what Mark Zuckerberg called an “embodied internet” when he announced last fall that Facebook would become Meta. A few months later, Microsoft revealed plans to acquire Activision Blizzard to “provide building blocks for the metaverse,” the company said. The downstream effects of all this technological ferment, Hoffman predicts, is that VR therapies, enabled by private sector investment, will quickly evolve into a standard treatment for pain.
On August 8, 2016, Robert Jester, a retired high school biology teacher in Greenport, NY, who worked as a chimney sweep — both to support his family and enjoy the beautiful view — drove to a nearby neighborhood for a quick job. The ladder he took was too short, but it seemed like a simple swing, so he decided to get on with the job anyway. He climbed to the top, the ladder slipped – and he fell to the hard ground below. The pain in his back was so bad he couldn’t see the rescuers bending over him; he could only see white light.