Three years ago, doctors in Toronto found that baby boys circumcised without local anesthesia were far more sensitive to pain six months later than their uncircumcised peers. A new study may reveal why: Painful trauma during infancy seems to rewire the nervous system permanently.
Neuroscientist M. A. Ruda and her colleagues at the National Institute of Dental and Craniofacial Research in Bethesda, Maryland, investigated this effect in newborn rats. The researchers injected the animals' hind paws with an irritant that causes several days of pain and swelling. When they reached adulthood, the rats experienced distinctly above-average responsiveness to pain. Autopsies revealed that their spinal cords had 25 percent more pain fibers linked to the hind paws than those in rats that were left alone. It's possible, says Ruda, that similar processes occur in humans exposed to painful medical procedures soon after birth. "There are a number of chronic pain states for which the physical causes are hard to identify," she says. "This is total speculation, but if your responses to pain are altered, you may be at a higher risk for some kinds of persistent pain."
