Modern pain science
Pain doesn’t always occur because the body is in direct danger. Earlier, Descartes’ theory held that pain is a simple signal traveling straight from the body to the brain – like clockwork, where an injury activates pain and the brain produces a reaction. But modern research has shown that pain isn’t that one-dimensional. There are activities that should, in theory, cause pain – such as a contortionist twisting their body into extreme positions – yet no pain is felt. At the same time, pain can occur in situations where the body faces no real threat at all, such as sitting at a computer.
This means that pain doesn’t depend only on signals coming from the body, but is a complex process constructed in the brain, shaped by emotions, beliefs, and past experiences.
Phantom pain
This new understanding of pain is based on various studies, starting with phantom pain – a phenomenon where up to 85% of people with an amputated limb feel pain in the body part that’s no longer there. These studies show just how complex pain really is, and explain why it’s sometimes called an illusion created by the brain. The fact that no signal travels to the brain from a missing limb proves just how large a role the brain plays in perceiving physical pain.
The role of thought in feeling pain
Other studies have shown that a person can feel pain even when their tissue isn’t actually damaged or in danger. In experiments, researchers manipulated participants’ perception using visual cues, making them believe their body was being harmed, and the brain generated pain to protect them. In one study, participants were shown either a red or a blue light before a metal rod touched the back of their hand. Although the rod’s temperature was always the same, those who saw the red light felt more pain, because red is associated with heat and blue with cold. In addition, those who watched the rod touch their hand reported more pain than those whose vision was blocked.
Injury without pain
There are also cases where an X-ray or MRI scan shows an injury, but the person feels no pain at all. Various studies have found that 30–80% of asymptomatic (pain-free) study subjects had a bulging spinal disc, 34% had a torn rotator cuff, and 30% had meniscus degeneration.
One case study described a soldier who had an X-ray taken for an unrelated reason, and a bullet was discovered in his neck, even though he felt no pain at all. It’s as if the brain had decided: “This isn’t dangerous, no need to generate pain.”
These and many other studies show that pain originates exclusively from the brain, not from pain receptors or nerve pathways in the body. Based on this new understanding, researchers began considering a two-sided model, in which the brain not only receives stimuli, but also decides whether they deserve a pain response.
The complexity of inputs
In this model, the brain is seen as a neuromatrix – a network of neurons with multiple inputs and outputs. The inputs include various sensations, not just touch, sight, hearing, and smell. There are also joint receptors called proprioceptors, which give the brain information about the body’s position in space. In addition, the neuromatrix is influenced by emotional inputs, which bring thoughts and feelings into the brain.
The brain constantly analyzes all these inputs and decides whether the environment is safe, or whether pain is a necessary response to a threat.
For example, touching a hot stove activates nociceptors – danger sensors that detect harmful stimuli. These stimuli can be thermal (something hot), chemical (a corrosive substance), or mechanical (a crushed finger).
When you touch something, an afferent signal travels from the tissue through the spinal cord to the brain, depending on what type of signal it is. If the signal is sensory, it reaches the sensory cortex. If it’s dangerous, it’s processed through nociception.
Outputs
At that point, the brain makes a decision through one of three possible outputs:
- Pain (you feel pain)
- Movement (you decide to move)
- A stress response (you feel anxious)
The first output, pain, directly contradicts Descartes’ model, which assumes pain originates from the body. In reality, a constant stream of sensations reaches the brain. The brain analyzes all these inputs, assesses the situation, and decides how to protect you, generating pain if necessary. Essentially, it determines whether the situation you’re in is dangerous and whether you need to change what you’re doing to avoid injury.
Pain is a calculated decision made by the brain
These and many other studies show that pain originates exclusively from the brain, not from pain receptors or nerve pathways in the body. Based on this new understanding, researchers began considering a two-sided model, in which the brain not only receives stimuli, but also decides whether they deserve a pain response.
This model treats the brain as a neuromatrix (a network of neurons) with multiple inputs and outputs. The inputs include various sensations, not just touch, sight, hearing, and smell. There are also joint receptors called proprioceptors, which give the brain information about the body’s position in space. In addition, the neuromatrix is influenced by emotional inputs, which bring thoughts and feelings into the brain.
The brain constantly analyzes all these inputs and decides whether the environment is safe, or whether pain is a necessary response to a threat.
According to this new understanding, pain is a complex experience shaped by our thoughts, emotions, beliefs, memories, stress levels, sensations, visual information, and much more – not simply a signal sent from body tissue.
Many people experience pain that is largely driven by high stress levels, mental health, lack of sleep, and other similar factors. But simply listing these factors isn’t useful on its own – what matters is understanding how they affect pain, and even more importantly, how to ease it.
Summary
The brain is the source of all your pain, and because the brain is complex, so is your pain. That said, the phrase “pain comes from the brain” is often misunderstood as “the pain is only in your head.” That’s not what’s being said here. While the brain creates pain, it isn’t imaginary – every person’s experience of pain is real and unique.
📖 Source: This post is based on Tom Walters and Glen Cordoza’s book Rehab Science: How to Overcome Pain and Heal from Injury (2023), which covers modern pain science and rehabilitation. If you want to go deeper into the topic, it’s well worth reading!
