According to a new investigation published online in the journal Current Biology, babies can recognize the difference between painful stimuli from general touch from approximately 35-37 weeks gestation – just before a baby would usually be born.

The investigation was funded by the Medical Research Council and the Wellcome Trust.

The researchers reveal that from 35 weeks of development, neural activity in the brain slowly changes from an immature state to an almost adult-like state. This change may suggest that neural circuitry permits babies to process pain as a separate feeling from touch.

Dr Rebeccah Slater, UCL Neuroscience, Physiology and Pharmacology, explained:

“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.”

At the University College Hospital Elizabeth Garrett Anderson Wing, investigators examined the brain activity of 46 babies of which 21 were born prematurely. This gave the investigations the chance to measure activity at various stages of human brain development, from infants at only 28 weeks development through to babies born ‘full term’ at 37 weeks.

The researchers measured the babies electrical brain activity using electroencephalography (EEG), whilst the infants were undergoing a routine heel lance – a standard procedure vital to collect blood samples for clinical use.

The EEG recorded a response to the hell lance of non-specific ‘neuronal bursts (general bursts of electrical activity in the brain) in the premature babies. The response for babies between 35-37 weeks changed to localized activity in specific areas of the brain, suggesting that they were able to feel the difference between painful stimulation separately to touch.

Dr Lorenzo Fabrizi, lead author of the paper from UCL Neuroscience, Physiology and Pharmacology, 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.”

Prior investigations have revealed that there is a similar shift from neuronal bursts to evoked potentials in the visual system at this time, indicating that 35-37 weeks is a time when important neural connections are formed between different parts of the brain.

Dr Slater said:

“It is important to understand how the human brain develops so that we can provide the best clinical care for hospitalized infants.”

Written by Grace Rattue