Infants' brains light up in response to pain in a similar way to adults, researchers have discovered, as they try to extend our understanding of the youngest patients' pain response.

Scientists from Oxford University in the U.K. found 18 of the 20 brain regions activated in adults experiencing pain were also active in infants.

In a small study, Rebeccah Slater of Oxford's pediatrics department and her team found when infants between one and six days old were placed in the MRI scanner, they usually fell asleep. The brain scans were done as a special retracting rod was placed on the bottom of their feet to create a sensation like being poked with a pencil.

"Our study suggests that not only do babies experience pain, but they may be more sensitive to it than adults," Slater said. "If we would provide pain relief for an older child undergoing a procedure, then we should look at giving pain relief to an infant."

Ten healthy adults most frequently described the pain as "pricking" and "sharp." None of the adults withdrew their leg as a reflex at any intensity while the infants did.

The scans suggested the infants' brains responded to a weak poke or stimulus as adults did to one four times as strong, the researchers reported in Tuesday's issue of the journal eLife.

Rachel Edwards, 33, from Oxford, felt the retracting rod, which she described as a "precise feeling of touch" before she gave permission for her son Alex to take part in the study.

Emotional side of pain explored

"People know so little about how babies feel pain, you can tell they are in distress from their reaction and I was curious about why they react in the way they do," Edwards said in a release.

"I fed him and put him down on this special bean bag that they suck all the air out of to help keep the babies' heads still. Then they put on earphones that cut out some of the sound but I think the noise actually soothed him. He was out for the count, he didn't wake up during the scanning and seemed really content afterwards."

Slater hopes to someday be able to develop systems to detect a "pain signature" in babies to test different pain relief options.

The vast majority of healthy, full-term infants respond to a painful stimulus such as a heel lance for blood tests or an injection, said Bonnie Stevens, associate chief of nursing, research at SickKids hospital in Toronto.

The study's authors pointed to a 2014 Dutch study of infants in intensive care, which found they experience an average of 11 painful procedures a day, for things like IV lines and blood draws.

Pain is more than sensory processing, Stevens said, and includes emotional and "affective" components such as unpleasantness. The Oxford study aims to build on what's known about how infants respond to pain to better understand their emotional and affective responses.

The researchers said patterns of brain activity may provide the most reliable substitute measure of pain compared with standard indicators such as facial expressions and increases in heart rate.

Stevens said the study introduces important new evidence.

"However, given the complex nature of pain in infants and other nonverbal populations, we still have much to learn about all types of infant pain responses. We also need to consider the context in which the pain is experienced (e.g. age of the infants, health status, nature of the painful stimulus, presence of care provider)," Stevens said in an email.

Stevens said it would be prudent to consider a broader approach to assess pain in infants given the advances won't automatically result in better pain prevention and treatment.

Denise Harrison, chair in nursing care of of Children, Youth and Families Children's Hospital of Eastern Ontario Research Institute and University of Ottawa, called the research "exciting and illuminating."

"While we continue to explore neural pathways of pain, we need to consistently use best pain management strategies, based on years of studies, mostly using behavioural responses — such as crying, facial expressions of pain," Harrison said in an email.

The study was funded by the Wellcome Trust.