Do Babies Feel Pain?

Do babies feel pain? Would you know if a baby was feeling pain?

It’s easy to think that perceiving infants’ pains would be obvious, but a growing body of research is suggesting that it is not very easy at all. With babies in neonatal units undergoing an average of ten painful procedures every day –from heel lances, to blood tests, to more extreme cases of open heart surgery-  the study of infant pain reduction is increasingly important, and demands attention from clinical neuroscientists.

On 24th November, Dr. Caroline Hartley, a Postdoctoral Researcher at Oxford Department of Paediatrics, joined us at our weekly lecture series to discuss her work on the development of new medical procedures and analgesics to prevent infants’ experience of pain.  There is evidence of long-term neurodevelopmental change as a result of repeated painful experience in early life. [1] Yet as recently as the 1980s, pain relief medication was not included as part of routine clinical practise [2]  and 60% of painful medical procedures are still carried out in babies without any pharmacological analgesics.

So why aren’t babies given anaesthetics?

Perhaps the most obvious reason is that babies can’t tell us when something hurts. And by the time they can, they’re not able to remember the experience. There are also risks posed by administering anaesthetics, particularly as the infants that need it most tend to be those already in medically unstable conditions. Finally, it has been argued that the infant brain has not yet developed sufficiently for painful stimuli to be processed in the same way as adults, who are thought to have a complex network of neural activity (a ‘pain matrix’) underlying their experience of pain. Infants’ brains are still far from fully developed, with the differentiation and maturation of many neurons and neuroglial cells still yet to occur. This has been assumed to mean that pharmacological analgesics aren’t necessary.

But is that true?

Can babies experience a feeling of pain that is comparable to that of adults? Additional research by Dr. Hartley suggests that the answer is yes [3]. They measured fMRI activity in both infants and adults who were exposed to noxious stimuli. In total, 20 different regions of the adult brain showed an increase in activity in response to pain. And of these 20 regions, 18 were also active in infants in pain. These areas were spread across the brain; including the primary somatosensory cortices, anterior cingulate cortex, thalamus, and insular cortices. Such a sophisticated and adult-like response to painful stimuli allows us to at least tentatively address the main question: yes, babies really do feel pain.

How do we know when babies are in pain?

Even since it became more widely accepted that infants can feel pain, the nature of this pain was still poorly understood. Until recently, doctors and researchers alike had to rely on surrogate measures to judge whether an infant was experiencing pain. These included changes in heart rate, respiratory rate and facial expression. However, research has shown that these measures do not adequately capture their experience of pain.

Oral administration of sucrose is often given to infants undergoing invasive procedures, for the primary reason that it reduces the behavioural expression of pain; they look less distressed. Yet, when the activity level of areas of the brain associated with responding to pain were examined, the sucrose was seen to be no more effective than simply giving the babies water [4]: in other words, not very. This suggests there are difficulties in using facial expression as a measure of pain experienced.

Dr Hartley’s recent research suggested that a limb withdrawal reflex may be a better indicator of when infants are experiencing pain [5]. They administered nociceptive stimuli of varying intensities to the heels of babies, and measured both EEG brain activity and limb withdrawal. They found an increase in brain activity that was tied specifically to painful the stimuli. Importantly, they also showed that the strength of the withdrawal reflex was related to both the intensity of the stimulus and the size of the neural pain response.

This could have huge implications. As the limb movement is an easily observable response, it may become a valuable way for infants’ experience of pain to be assessed.

 

caroline hartley
Dr. Caroline Hartley, Postdoctoral Researcher at Oxford Department of Paediatrics.

References:

[1] Hermann, C., Hohmeister, J., Demirakca, S., Zohsel, K., Flor, H. (2006). Long-term alteration of pain sensitivity in school-aged children with early pain experiences. Pain; 125: 278–85.

Hohmeister, J., Demirakca, S., Zohsel, K., Flor, H., Hermann, C. (2009). Responses to pain in school-aged children with experience in a neonatal intensive care unit: cognitive aspects and maternal influences. European Journal of Pain; 13: 94–101.

[2] Anand, K.J., & Hickey, P.R. (1987). Pain and its effects in the human neonate and fetus. The New England journal of medicine, 317(21):1321-9.

[3] Goksan, S., Hartley, C., Emery, F., Cockrill, N., Poorun, R., Moultrie, F., Rogers, R., Campbell, J., Sanders, M., Adams E., Clare S., Jenkinson M., Tracey, I., Slater,R. (2015). MRI reveals neural activity overlap between adult and infant pain. ELife Sciences, 4:e06356.

[4] Slater, R., Cornelissen, L., Fabrizi, L., Patten, D., Yoxen, D., Yoxen, J., Worley, J., Boyd, S., Meek, J., Fitzgerald, M. (2010). Oral sucrose as an analgesic drug for procedural pain in newborn infants: a randomised controlled trial. The Lancet, 376(9748), 1225-1232.

[5] Hartley, C., Goksan, S., Poorun, R., Brotherhood, K. Mellado, G.S., Moultrie, F., Rogers, R., Adams, R., Slater, R. (2015). The relationship between nociceptive brain activity, spinal reflex withdrawal and behaviour in newborn infants. Scientific Reports, 5: 12519.

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