A baby’s pain registers in the brain

An electrode on top of a newborn’s scalp, near the soft spot, can measure when the baby feels pain. The method, described online May 3 in Science Translational Medicine, isn’t foolproof, but it brings scientists closer to being able to tell when infants are in distress.

Pain assessment in babies is both difficult and extremely important for the same reason: Babies don’t talk. That makes it hard to tell when they are in pain, and it also means that their pain can be more easily overlooked, says Carlo Bellieni, a pediatric pain researcher at the University Hospital Siena in Italy.

Doctors rely on a combination of clues such as crying, wiggling and facial grimacing to guess whether a baby is hurting. But these clues can mislead. “Similar behaviors occur when infants are not in pain, for example if they are hungry or want a cuddle,” says study coauthor Rebeccah Slater of the University of Oxford. By relying on brain activity, the new method promises to be a more objective measurement.

Slater and colleagues measured brain activity in 18 newborns between 2 and 5 days old. Electroencephalography (EEG) recordings from electrodes on the scalp picked up collective nerve cell activity as babies received a heel lance to draw blood or a low-intensity bop on the foot, a touch that’s a bit like being gently poked with a blunt pencil. One electrode in particular, called the Cz electrode and perched on the top of the head, detected a telltale neural spike between 400 and 700 milliseconds after the painful event. This brain response wasn’t observed when these same babies received a sham heel lance or an innocuous touch on the heel.

The Cz electrode detected similar brain responses to painful procedures in tests of 14 other newborns. Loud sounds, flashing lights and nonpainful touches didn’t elicit the same response in those newborns. What’s more, this brain signature changed when pain-relieving gel was used in another group of 12 babies who were on average 25 days old. After treatment with the topical anesthetic tetracaine, babies’ brain responses to foot thumps were smaller than when the taps were delivered to unmedicated feet.

On average, babies born prematurely between 34 and 36 weeks gestation showed similar neural responses to pain. It’s unclear whether this presumed pain signature would be present in babies born earlier or in older infants, says Slater.

In its current form, the method isn’t reliable enough to be used as a definitive readout of pain in individual babies. That’s because not all babies’ brains responded to pain similarly. Ten of 28 babies who had heel lances didn’t show this neural signature, the researchers report.

And the brain signature didn’t always track with other pain indicators. Of the 17 babies who indicated pain by changing facial expressions during a presumably painful event, 13 also showed the brain activity signature and four did not. Of the 11 babies who did not change expressions, five showed the brain signature and six did not. Slater says that a combination approach that relies on multiple indicators of pain might be useful.  

Even if this current EEG method is improved, it might not be clinically useful, Bellieni points out. A method that measures quick and severe pain can’t be used to change a painful situation in real time. “When you get the results, the procedure is already over,” he says. Still, he suspects that such a measurement will be a valuable research tool.