New study reveals infants feel pain before they can understand it

The findings, published in the journal Pain, offer new insights into how infants' brains develop the ability to process pain and have significant implications for neonatal care, especially for preterm babies.

The research, led by Professor Lorenzo Fabrizi of UCL's Department of Neuroscience, Physiology and Pharmacology, explored how different components of pain perception emerge in early life.

"Pain is a complex experience with physical, emotional, and cognitive elements," Fabrizi explained, adding, "In adults, the brain regions involved in pain, known collectively as the 'pain connectome', work together to create the full experience. In newborns, this network is still maturing, which may mean their experience of pain is vastly different from ours."

The team analysed brain scans from 372 infants, many born prematurely, using data from two of the largest infant brain imaging projects: the Developing Human Connectome Project and the Human Connectome Project.

All infants were scanned within their first two weeks of life to ensure that the results reflected natural brain development rather than the influence of postnatal experiences.

Researchers focused on three specific brain networks related to pain processing: Sensory-discriminative: Responsible for identifying and locating pain. Affective-motivational: Governs the emotional response to pain. Cognitive-evaluative: Handles the interpretation and judgment of pain.

Findings showed that the sensory-discriminative network matures first, typically between 34 and 36 weeks after conception.

This means that even premature infants can detect pain stimuli, though they may struggle to pinpoint where the pain is coming from.

Next, the affective-motivational network, which gives pain its unpleasant emotional quality, reaches functional maturity around 36 to 38 weeks.

However, the cognitive-evaluative network, crucial for understanding the significance of pain, doesn't fully mature until after 42 weeks, meaning that full-term newborns still lack the brain development needed for complete pain comprehension.

These findings are especially relevant in medical settings. A prior study from the same team in 2023 found that premature infants do not show signs of habituating to repeated medical procedures; they continue to react as though the pain is new each time. This latest study suggests that the immaturity of certain brain networks could explain that phenomenon.

"Our results suggest that preterm babies may be particularly vulnerable to painful medical procedures during critical stages of brain development," said Professor Fabrizi, adding, "This highlights the need for pain management strategies that are tailored to a baby's stage of neural development."

The study was funded by the UK's Medical Research Council and involved collaboration with researchers from UCLH and King's College London.

These findings could help reshape clinical protocols for neonatal care, especially for the most vulnerable infants, by encouraging more precise pain management and timing of interventions.