Diffuse Noxious Inhibitory Control (DNIC) is one of the mechanisms we can use for managing pain. That name is a mouthful, so I call these counter-irritants. (Read my post on birth combs as a DNIC tool here.) The principle is that if a laboring mom adds a pain or discomfort on her body during a contraction (like biting her lip, pressing her fingernails into her palm, or putting ice on her back), that helps to distract her brain from the pain. TENS, sterile water injections, acupressure, and birth combs are all DNIC tools for labor.
One theory for why these are effective is that the pain from these sensations causes a release of endorphins, endogenous opiates that help to reduce our perception of pain.
Another has to do with how the brain processes stimuli coming in on various pathways. (This is similar to the Gate Control mechanism of pain, which says that when we provide stimuli on fast-moving nerve pathways – like through sound, smell, touch with our sensitive fingers and toes – then those block some of the pain coming in on slower pathways – like labor pain.)
Chaillet, et al says that DNIC primarily reduce the intensity of pain. I believe that they can also help to reduce the unpleasantness of the pain. (see my post here for the difference between the intensity of pain and the unpleasantness of pain.) If mom is in control of the counter-irritant, it may give her more of a sense of control over the labor pain. She may feel like she can’t escape the labor pain (it’s highly “unpleasant”) but that she could stop biting her lip anytime she wants… being in control of something is better than feeling totally out of control. It’s one way of “working with labor pain.”
In childbirth classes, we can talk about counter-irritants by suggesting options to the pregnant parent (ice, squeezing something, TENS). We can use the concept to better explain sterile water injections (some parents are mis-educated in advance, and think that the injections themselves relieve pain… they’re shocked at how much the injections hurt! So, we want to explain in advance that they do hurt… like a bee sting… and that’s the idea, because they trigger an endorphin release.
In classes, we can also let the support person know that some people in labor develop a spontaneous ritual where they are causing pain to themselves (like pulling their hair)… help the partner understand that the person in labor is looking for counter-irritant – an uncomfortable sensation to distract her from the pain, and they can help her find one that gives that counter-stimulation but doesn’t harm her (like squeezing birth combs).
In the Bonapace method (I’ll post on that tomorrow), the DNIC mechanism that is taught is for the partner to do painful pressure on acupuncture trigger points. I personally prefer using only counter-irritant techniques that the person in labor applies and controls. I personally don’t like to teach partners to do anything painful to a woman, even if it might have benefit for labor pain. (A licensed massage therapist who has been clearly trained in safe high pressure massage I have no concerns about.) If I were to teach this in a class, I would set clear expectations that the laboring woman controls this firm massage – she asks for it to be done, and if she doesn’t like it, she tells her partner to stop, and her partner should stop.