"A major challenge in analgesic trials in the infant population is definition of a reliable, quantitative outcome measurement of pain because verbal reports and visual analogue scales cannot be used. The most commonly used outcome measures are based on behavioural and physiological observations, and many validated composite pain measurement instruments, such as the premature infant pain profile (PIPP), are based on these observations. These methods might not, however, be an appropriate outcome measure for neonatal analgesic trials because they are largely based on human observation and judgment,and, whereaspainexperienceandpainbehaviourarelinked in adults,they might not be linked in neonates. For example, infants who do not display a change in facial expression after tissue damaging procedures might still display significant cortical responses, which suggests that infant behaviour is not a simple indication of pain activity in the brain. Many conditions, such as immaturity, neurological damage, and maternal drug misuse, can affect integrated sensorimotor function and consequent behaviour, but might not necessarily affect sensory pain processing.

"The results show that although, as previously reported, sucrose significantly reduces the PIPP score—a composite observational behavioural and physiological measure—it has no effect on the neural activity in sensory pain circuits in the brain or the spinal cord. Although true pain perception cannot be measured in non-verbal populations, neural activity in nociceptive pathways is a more direct measure than behavioural and physiological assessment. The finding that sucrose does not change neural activity strongly suggests that pain perception is not affected by this intervention.

In conclusion, our results show that although oral sucrose does reduce observed pain behaviour, it has no significant effect on the magnitude of spinal nociceptive reflexes or on the acute activation of pain networks in the brain. Sucrose seems to blunt facial expression activity after painful procedures, but our data suggest that it does not reduce direct nociceptive activity in central sensory circuits, and therefore might not be an effective analgesic drug.