Investigating paediatric pain: Q & A with Professor Maria Fitzgerald
Newborn babies, particularly those in intensive care, undergo many essential clinical procedures which would be painful for you or me. Yet until the late 1980s it was widely believed that newborn babies did not feel pain. This belief has changed considerably over the past 25 years, but exactly how pain is processed in infants is still being researched. Professor Maria Fitzgerald, UCL, studies how babies experience pain, and whether this could have an impact on their development. Nancy Wilkinson met her to find out more.
Why was it common to think babies could not feel pain?
A newborn infant only has a limited range of behaviours: crying, reflex movements and some facial expressions, for example. Infants display these behaviours in response to a range of stimuli – a loud sound, hunger, isolation – and pain. Previously it was thought that because the infant’s response to pain was no different to the response to other stimuli, we didn’t need to worry about it.
There was also a very simplistic view of memory until the 1980s. It was thought that because we don’t remember anything from when we were babies, we don’t process it and it isn’t important.
We have moved on in many ways, now. We have found there is a distinct sensory pathway for painful stimuli in newborn infants, so it was wrong to say they couldn’t feel pain.
What does your research focus on?
We study the underlying neural mechanisms at the very beginning of life. We’re interested in how the sensory system at that stage distinguishes between a gentle touch, intense pressure, or something that is tissue damaging and may produce pain, otherwise called a noxious stimulus.
What is the difference between a noxious stimulus and pain?
Pain is a perception. It is something that is constructed in your brain; it is an experience. If someone were to stick a pin in your thumb, the pain is not in your thumb, it is what you perceive with your mind. A noxious stimulus is a potentially tissue damaging stimulus, that activates a specific response from your nervous system, but doesn’t necessarily feel painful. It might seem a bit pedantic, but it is in fact a very important difference when we consider the underlying pathways in the brain.
Do you work with human infants?
Yes. In the laboratory we use animal models, analysing the circuits that underlie how mammalian brains process pain, but we also collaborate with neonatologists at University College London Hospital (UCLH). With the permission of parents, we record activity in the nervous system of newborn babies undergoing painful clinical procedures, like those in intensive care.
How do you do that?
We use electroencephalography (EEG) to record activity in the brain. It is a non-invasive technique that measures electrical activity, mainly in the cortex of the brain. It is more practical than methods such as fMRI as it measures brain activity without a time delay, and is much easier to use on newborn babies. For fMRI, the infants need to be completely still, which is very difficult to achieve, and it is very noisy inside the machine, which can be unpleasant. There is also an issue of control cases: most parents really don’t want their baby to go into a giant magnet [fMRI machine], when they are only a few hours old, just to be a control for an experiment.
What results have you got from your research on animals?
In our animal models, we have been able to show that the pain sensory circuits, or nociceptive circuits, in young animals are not the same as those in adults.
The most important discovery in the past couple of years has been that inhibitory neurons in nociceptive circuits, those that act to dampen stimuli down, develop much later than other neurons. This means the infant nervous system is a little like an open door: it lacks the ability to switch attention between stimuli, localise where a stimulus is coming from, or control how strong the stimulus is. Using EEG, we have been able to show that, in response to noxious stimulation, the neural activity in the newborn brain is clearer and longer lasting than in an adult brain. But it’s important to note that we do not know that this means infants experience more pain – it would be very difficult to determine that.
What’s next for the group?
Many toddlers have to undergo a lot of painful procedures, like inoculations. We would like to extend our animal and human studies to an older age group. This is all very new, but it’s something we’re very excited about. We hope that, by giving it a solid scientific basis, we will be able to have a big impact on the measurement and treatment of paediatric pain.
More information on pain processing in newborn infants and Professor Fitzgerald’s research can be found in this feature article by Mun-Keat Looi, Online Editor for the Wellcome Trust.