The study looked at 10 healthy infants aged between one and six days old and 10 healthy adults aged 23-36 years. Infants were recruited from the John Radcliffe Hospital, Oxford (UK) and adult volunteers were Oxford University staff or students.
During the research babies, accompanied by parents and clinical staff, were placed in a Magnetic Resonance Imaging (MRI) scanner where they usually fell asleep. MRI scans were then taken of the babies’ brains as they were ‘poked’ on the bottom of their feet with a special retracting rod creating a sensation ‘like being poked with a pencil’ – mild enough that it did not wake them up. These scans were then compared with brain scans of adults exposed to the same pain stimulus.
The researchers found that 18 of the 20 brain regions active in adults experiencing pain were active in babies. Scans also showed that babies’ brains had the same response to a weak ‘poke’ (of force 128mN) as adults did to a stimulus four times as strong (512mN). The findings suggest that not only do babies experience pain much like adults but that they also have a much lower pain threshold.
The research was funded by the Wellcome Trust and is reported in the journal eLife.
‘Up until recently people didn’t think it was possible to study pain in babies using MRI because, unlike adults, they don’t keep still in the scanner!’ said Dr Rebeccah Slater of Oxford University’s Department of Paediatrics, lead author of the report. ‘However, as babies that are less than a week old are more docile than older babies, we found that their parents were able to get them to fall asleep inside a scanner so that we could study pain in the infant brain using MRI.’
‘This is particularly important when it comes to pain: obviously babies can’t tell us about their experience of pain and it is difficult to infer pain from visual observations. In fact some people have argued that babies’ brains are not developed enough for them to really ‘feel’ pain, any reaction being just a reflex – our study provides the first really strong evidence that this is not the case.’
The researchers say that it is now possible to see pain ‘happening’ inside the infant brain and it looks a lot like pain in adults.
As recently as the 1980s it was common practice for babies to be given neuromuscular blocks but no pain relief medication during surgery. In 2014 a review of neonatal pain management practice in intensive care highlighted that although such infants experience an average of 11 painful procedures per day, 60% of babies do not receive any kind of pain medication.
‘Thousands of babies across the UK undergo painful procedures every day but there are often no local pain management guidelines to help clinicians. Our study suggests that not only do babies experience pain, but they may be more sensitive to it than adults,’ said Dr Slater. ‘We have to think that if we would provide pain relief for an older child undergoing a procedure then we should look at giving pain relief to an infant undergoing a similar procedure.’
Dr Slater added: ‘Recent studies in adults have shown that it is possible to detect a neurological signature of pain using MRI. In the future we hope to develop similar systems to detect the ‘pain signature’ in babies’ brains: this could enable us to test different pain relief treatments and see what would be most effective for this vulnerable population who can’t speak for themselves.’
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