Gatekeepers of pain: how your body decides what hurts

Pain is an unpleasant bodily sensation that’s usually linked to actual or potential tissue damage. It often acts as the body’s warning system, protecting us from further harm. Now picture this: you hit your leg, and it hurts—but then you instinctively start rubbing it, and the pain begins to ease. Why does that happen? That’s where the Pain Gate Theory (also known as The Gate Theory of Pain, or The Gate Control Theory of Pain) comes in. It’s one of the most fascinating ideas in pain science because it explains how pain isn’t just about injury— it’s also about how our nervous system processes it. Pain can vary greatly between individuals and even in the same person under different circumstances. This variation is due to the fact that pain is not just a physical experience, but also influenced by emotions, attention, and context.

The Pain Gate Theory was first coined in 1965 by Ronald Melzack and Patrick Wall to explain this phenomenon. It states that a stimulus must travel through the substantia gelatinosa in the dorsal horn of the spinal cord, the transmission cells and the fibres in the dorsal column in order to have an effect. The substantia gelatinosa acts as a ‘gate’, mediating which signals are able to pass through the nervous system to the brain. As to whether the gate closes is influenced by an array of factors. 

How does it work?

The below figure depicts the relationships in The Pain Gate Theory. The gate mechanism is influenced by the activity of the larger diameter fibres (A-beta) which usually inhibit transmission and the small diameter fibres (A-delta and C) which increase transmission.

Take our analogy from earlier about rubbing your leg: when you do this, the large fibres carrying non painful stimuli like touch and pressure are activated. This causes the gate to be ‘closed’ which blocks the pain signals being transmitted by the small fibres.

This concept is so interesting as it opens doors to viewing pain holistically; pain is influenced by touch, thoughts and emotions, which explains why you may not notice pain as much when your super excited about something or why placebos have been proven to work in some cases.

In a clinical sphere, this theory has opened the door to many pain management techniques, for example Transcutaneous Electrical Nerve Stimulation (TENS), which selectively stimulates A-beta fibres leading to a consequential inhibition in A-delta and C fibres, preventing pain-related signals reaching the brain. It also has been utilised in physiotherapy, labour and chronic pain treatments. 

One main limitation of this model is its inability to explain certain types of pain like phantom limb since it relies on the assumption that pain requires an input from a limb to the spinal cord. This has led to the development of more advanced models like the neuromatrix model which acknowledges the fact that the brain can create pain on its own.

In conclusion, the bottom line is that The Pain Gate Theory was groundbreaking in our understanding of how pain works. Understanding pain as a brain-and-body experience opens the door to innovative treatments that may one day make pain more manageable, or even preventable.

Written by Blessing Amo-Konadu

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Merrick, Mark. “Gate Control Theory - an Overview | ScienceDirect Topics.” Sciencedirect.com, 2012, www.sciencedirect.com/topics/medicine-and-dentistry/gate-control-theory.

Tashani, O, and M Johnson. “Transcutaneous Electrical Nerve Stimulation (TENS). A Possible Aid for Pain Relief in Developing Countries?” Libyan Journal of Medicine, vol. 4, no. 2, 10 Dec. 2008, pp. 77–83, www.ncbi.nlm.nih.gov/pmc/articles/PMC3066716/pdf/LJM-4-062.pdf, https://doi.org/10.4176/090119.

The British Pain Society. “What Is Pain?” Britishpainsociety.org, July 2020, www.britishpainsociety.org/about/what-is-pain/.

Trachsel, Lindsay A., et al. “Pain Theory.” PubMed, StatPearls Publishing, 17 Apr. 2023, www.ncbi.nlm.nih.gov/books/NBK545194/