Buzz
When you accidentally trap your fingers in a car door or bump your funny bone against a wall, your initial instinct might be to suck on your finger or rub your elbow. This instinctive action isn’t just a reflex—it’s a surprisingly effective way to temporarily calm the pain signals reaching your brain.
But what makes this work? To understand this, we need to look at the prevailing theory on how pain is transmitted throughout the body.
In the 17th century, French philosopher and scientist René Descartes suggested that the body contained specific pain receptors that 'rang a bell in the brain' when triggered by pain. However, according to Lorne Mendell, a professor of neurobiology and behavior at Stony Brook University in New York, no research has yet successfully pinpointed receptors in the body that solely respond to painful stimuli.
'You can activate certain nerve fibers that can lead to pain, but under other circumstances, they don't,' says Mendell. In essence, the same nerve fibers that transmit pain signals are also responsible for conveying other sensations.
In 1965, two MIT researchers, Patrick Wall and Ronald Melzack, introduced the gate control theory of pain, a concept that continues to be relevant today. Mendell, a researcher in the neurobiology of pain who collaborated with both Wall and Melzack, explains that their studies showed that the experience of pain is primarily determined by the balance of stimuli on different types of nerve fibers.
'The idea was that certain fibers, which increased the input, opened the gate, while others, which reduced the input, closed the gate,' Mendell explains. 'So, imagine a gate control at the entrance of the spinal cord, which could either be open to allow pain or closed to lessen pain.'
The gate control theory was expanded in 1996 when neurophysiologist Edward Perl discovered that cells possess nociceptors—neurons that detect tissue-damaging stimuli or the presence of tissue damage.
There are two primary types of nerve fibers—large and small—where the large fibers transmit non-nociceptive (non-pain) information, and the small fibers convey nociceptive (pain) information.
Mendell describes that in experiments where electric stimulation is applied to nerves, the largest fibers are the first to react as the intensity of the current increases. As the stimulus becomes stronger, smaller fibers start to activate. 'When you apply this at a low intensity, the patient feels the stimulus, but it’s not painful,' he explains. 'However, as you increase the intensity, a point is reached where the patient will suddenly say, 'This is painful.'"
Thus, 'the idea was that shutting the gate was something that the large fibers produced, and opening the gate was something that the small fibers produced.'
Now, back to your pain. When you suck on a jammed finger or rub a bruised shin, you're activating the large fibers with 'counter irritation,' Mendell says. This leads to 'a reduction in the signal strength, or the volume of signals traveling through the incoming fibers. You essentially close the gate. That’s what eases the pain.'
This idea has spawned 'a huge industry' around treating pain with mild electrical stimulation, according to Mendell, aiming to stimulate those large fibers with the hope that they’ll close the gate on the pain signals sent by the small fibers.
Although counter irritation might not relieve the pain from a major injury, it can be quite useful for minor discomforts like a bruise or a stubbed toe.
