There has been considerable debate over the existence of pain in newborns and its management. As late as the mid-1980's, surgery was performed on infants without benefit of anesthesia, the belief being that even if babies did experience pain, they would forget about it. Since then, studies of the biological response to pain and the facial expressions of newborns during traumatic procedures document that they do indeed respond to pain. Today, pain from traumatic surgeries in newborns is carefully managed with anesthesia and analgesics.
Scientists have learned that by 24 weeks gestation, very immature pain transmission pathways are already in place. The development of these pathways continues postnatally. What newborns lack are fully developed and functional pain inhibitory systems. These typically develop several weeks after a full-term baby is born.
"Unlike other sensory modalities such as vision and hearing that require the input of sight and sound for their appropriate development, pain pathways normally develop in the absence of, or with little exposure to, painful stimulation. However, medical procedures shortly after birth can expose the nervous system to pain, the developmental effects of which we are just learning," said Dr. Ruda.
In their study, Dr. Ruda and her colleagues used newborn rat pups to explore the effect of tissue injury and pain on the development of pain pathways. An irritant was injected into the left hind paw of the pups to induce swelling. One group received the injection when they were 1 day old, an age equivalent to 24 weeks gestation in humans. A second group received the injection 14 days after birth, equivalent to adolescence in humans. Swelling and redness occurred shortly after the injection and persisted for 5-7 days in both groups.
Contact: Jody Dove
NIH/National Institute of Dental and Craniofacial Research