What does the gate control theory of pain have to do with a mental health blog? Well, co-occurring mental illness and chronic pain are remarkably common. For example, among people with fibromyalgia, over 50% experience depression. The rates of anxiety disorders are also over 50%. People with depression and anxiety disorders are also at increased risk to develop a pain disorder.
The gating process
So, how does pain actually work? Pain receptors (called nociceptors) get stimulated, and that message travels to the spinal cord and up to the brain. It’s not as simple as that, though. There is a gating process that determines which pain signals get through, and that’s the basis of the gate control theory, which was initially developed in 1965.
The gating action happens at a part of the spinal cord called the dorsal horn. Several kinds of nerves converge here and try to pass on their signals. Small nerve fibres carry pain signals, while large nerve fibres carry other sensory information. Then there are inhibitory interneurons connecting to both large and small fibres, as well as projection neurons that travel on up to the brain.
The inhibitory interneurons play the role of gates. If there is a strong pain stimulus, it closes the gate to the large fibres and their sensory info, allowing the pain signals to pass through and get transmitted up the spinal cord. If there’s a stronger stimulus from the large fibres, that sensory signal gets passed along rather than the pain signal.
Factors that affect pain perception
This may explain why acupuncture is helpful (albeit not in the way it’s claimed to work). It stimulates sensory nerves without producing pain, which can help to drown out some of the pain signals. Transcutaneous electrical nerve stimulation (TENS) accomplishes the same purpose.
The gates are also affected by signals sent from the brain down the spine, which introduces a number of other factors that can influence the perception of pain. Stress, tension, inactivity, and increased focus on pain can open up the gates to let pain signals through. Catastrophizing around pain promotes hypervigilance and heightens the focus on pain, which leads to more pain signals being transmitted to the brain. Relaxation, good mood, physical activity, and focus on activities rather than the sensation of pain have the opposite effect. Cognitive behavioural therapy (CBT) for pain likely works at least in part by affecting this aspect of the gate control theory.
What I find most interesting about this theory is that it suggests that the most effective approach to managing chronic pain is multi-pronged. Sure, medications can affect the transmission of pain signals, but the other ways we stimulate our bodies and what we do with our minds matter as well – and not just in a dismissive “just choose to be happy” kind of way, but in a logical, biologically based way.
Do you have a co-occurring mental illness and chronic pain? Does gate control theory fit with how you conceptualize your pain disorder?
You may also be interested in the post CBT for Chronic Pain.