Woolf was conducting his own experiment in Wall’s lab, applying painful stimuli to the rats’ hind legs. The animals developed large pain “fields” that could easily be activated months later with a light tap or gentle warmth, even in places that were not directly touched. “I was changing the function of the nervous system, so its properties were altered,” says Woolf. “Pain was not simply a measure of peripheral pathology,” he concluded; it “could also be the consequence of an abnormal amplification in the nervous system – this was the phenomenon of central sensitization”. Prior to this discovery, he says, “the feeling was always pain is a symptom that reflects a disease, and now we know that pain is often a consequence of a pathological condition of the nervous system itself.” Some conditions, such as rheumatoid arthritis, may exhibit both peripheral pathology and central sensitization. Others, like fibromyalgia, characterized by pain throughout the body, are considered solely a problem of the central nervous system itself.
A better understanding of how chronic pain alters the central nervous system has emerged since Woolf’s experiment. A.Vania Apkarian’s Pain Lab at Northwestern University found that when back pain persists, brain activity shifts from sensory and motor regions to areas associated with emotions, including the amygdala and seahorse. “It’s now part of the internal psychology,” Apkarian says, “a negative emotional cloud setting in.”
The brain itself is changing. Patients with chronic pain may experience significant loss of gray matter in the prefrontal cortex, the region of the brain responsible for attention and decision-making behind our forehead, as well as in the thalamus, which relays sensory signals; both areas are important in the treatment of pain. Excitatory neurotransmitters increase and inhibitors decrease, while glial cells and other immune cells drive inflammation; the nervous system, unbalanced, magnifies and prolongs the pain. The system goes haywire, like an alarm that sounds even when there is no threat, even when the pain is no longer protective. Instead, it just causes more pain – and the longer it goes on, the more deeply systemic it becomes and the harder it is to resolve.
There’s a popular saying in neuroscience that when neurons fire together they start to connect, an example of neuroplasticity in action. But if our brains are truly plastic, what is shaped there can be reshaped. Therapies that target the brain rather than the sore back or knee — whether through psychology, drugs, direct brain stimulation, or virtual reality — could in theory undo chronic pain.
In the 1990s, Hunter Hoffman, a cognitive psychologist at the University of Washington, began using virtual reality to provide relief to burn patients who had their dressings changed – an excruciating ordeal difficult to treat. “No one was using virtual reality to reduce pain for patients before us,” he says. In his virtual reality program, called SnowWorld, patients who walked through the winter scene, throwing snowballs at the penguins, reported that their relief was similar to what they got from intravenous opioids. Brain scans confirmed these findings: virtual reality and opioids each caused remarkable reductions in neural activity in areas related to pain.
Unlike most medications and surgeries, virtual reality has far fewer side effects, primarily nausea and motion sickness. Headsets now cost a fraction of what they once cost, and the graphics are significantly improved, resulting in more immersive experiences and fewer potential side effects. What’s more, Hoffman says, “every major IT company is pumping billions of dollars into virtual reality as a kind of internet” – what Mark Zuckerberg called an “internet embodied” when he announced last fall that Facebook became Meta. A few months later, Microsoft unveiled its intention 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, fueled by private sector investment, will rapidly develop into a standard pain treatment.
On August 8, 2016, Robert Jester, a retired high school biology teacher in Greenport, NY, who moonlighted as a chimney sweep – both to support his family and to enjoy the beautiful views – traveled to a nearby neighborhood to quick work. The ladder he took was too short, but it looked like a simple sweep, so he decided to continue the work anyway. He climbed to the top, the ladder slipped – and he fell to the hard ground below. The pain in his back was so intense he couldn’t make out the paramedics hunched over him; he could only see white light.