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Babies more than two weeks premature show same brain responses to pain and touch

9 September 2011

Babies develop their ability to distinguish painful stimuli from general touch during the last two weeks of the normal gestation period, new research funded by the Wellcome Trust and the Medical Research Council suggests.

In a study published online in the journal 'Current Biology', scientists show that certain patterns of activity in the brain mature from 35 weeks of development - towards the end of the standard 37-week gestation. This change in neural circuitry may allow babies to process pain as a separate sensation from touch.

Dr Rebeccah Slater University College London (UCL), said: "Premature babies who are younger than 35 weeks have similar brain responses when they experience touch or pain. After this time there is a gradual change, rather than a sudden shift, when the brain starts to process the two types of stimuli in a distinct manner."

Scientists looked at the brain activity of 46 babies at the University College Hospital Elizabeth Garrett Anderson Wing. Twenty-one babies in the study were born prematurely, giving scientists the opportunity to measure activity at different stages of brain development, from babies at just 28 weeks of development through to those born 'full term' at 37 weeks.

Using electroencephalography (EEG), the scientists measured electrical brain activity as the babies were undergoing a routine heel lance - a standard procedure essential to collect blood samples for clinical use.

In the more premature babies the EEG recorded a response to the heel lance of non-specific 'neuronal bursts' - general bursts of electrical activity in the brain. After 35-37 weeks, babies responded with more localised activity in specific areas of the brain, indicating that they were now perceiving painful stimulation as separate to touch.

Dr Lorenzo Fabrizi, lead author of the paper at UCL, said: "We are asking a fundamental question about human development in this study: when do babies start to distinguish between sensations? In very young brains all stimulations are followed by 'bursts' of activity, but at a critical time in development babies start to respond with activity specific to the type of stimulation.

"Of course, babies cannot tell us how they feel, so it is impossible to know what babies actually experience. We cannot say that before this change in brain activity they don't feel pain."

Previous studies have shown that there is a similar shift from neuronal bursts to localised activity in the visual system at this time, suggesting that 35-37 weeks post-conception is a time when important neural connections are formed in the brain.

Dr Slater added: "It is important to understand how the human brain develops so that we can provide the best clinical care for hospitalised infants."

Image: A newborn baby. Credit: Anthea Sieveking/Wellcome Images

Reference

Fabrizi L et al. A shift in sensory processing which enables the developing human brain to discriminate touch from pain. Curr Biol 8 September 2011 [epub]

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