Pain is a universal human experience. Although we often consider pain as a measure of tissue damage, correlated with the degree of injury, this is not the case at all.The role of brain when we feel pain is that pain is a protective system that allows us to change our behavior before damage occurs. All pain, no matter how it feels, sharp or dull, strong or mild, is always a construct of the brain and is uncorrelated with tissue damage.
If there is good reason to believe that protection is required, then our brain makes pain. Sometimes, however, this pain is not useful; our nervous system becomes overprotective, producing unnecessary warning signals that cause unhelpful persistent pain.
All around our body, there are sensory neurons called nociceptors. Their function is to detect actual or potential tissue-damaging events, such as thermal, mechanical or chemical stimuli, and send a “possible threat” signal to the spinal cord. Here, a second neuron takes the message and travels up the spinal cord to the brain.
The brain makes sense of this message by drawing information from current and past experience and from the state of our mind: Where are we? What are we doing? What can we see, smell, hear? Have we been here before? What happened last time? How did we solve it? Are we stressed, frightened, relaxed?
The brain assesses how dangerous the situation is and decides on a course of action. If it perceives the situation as potentially harmful, it will produce pain to draw our full attention to it. Conversely, if the brain believes there is no need for protection, it will not produce pain. That is to say, pain is not produced in the body; it is produced in the brain. A danger message coming from the body is neither sufficient nor necessary to produce pain.
The role of brain when we feel pain is that Pain emerges with the activation of a neurotag, a network of neurons in the brain. Different neurotags can wire together to share the same brain cells; hence, the activation of one neurotag can trigger the activation of another. For example, the neurotag related to low back pain may share brain cells with the neurotag involved in how we think and feel about our low back. If we believe that our back is fragile or damaged, perhaps due to an old injury or a past trauma, that will increase the activation of the back pain neurotag.
If we expect that something dangerous will happen to our low back and we tend to have a catastrophizing aptitude, the pain neurotag will consequently activate and produce more pain. Any credible evidence of danger to our back — for example, suggestive language used by our health professional or viewing models of slipped discs — will turn on or turn up the pain.
When pain persists for months or years, the pain neurotag becomes more sensitive and activates with smaller stimuli. For people who have suffered from chronic low back pain for a long time, watching someone bending forward to pick up a box may be enough of a stimulus to feel back pain. And their pain is real.