Washington: Babies can distinguish pain from general touch after around 35 to 37 weeks of gestation, just before they are born.
Scientists show that brain cell (neural) activity gradually changes from an immature state to a more adult-like state from 35 weeks of development.
This change may indicate that neural circuitry allows babies to process pain as a separate sensation from touch, the journal Current Biology reports.
Rebeccah Slater, neuroscientist at the University College London, 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," added Slater, according to a University College statement.
Scientists looked at the brain activity of 46 babies at the University College Hospital of which 21 were born prematurely.
This permitted them 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.
Scientists measured babies` electrical brain activity when they were undergoing a routine heel lance -- a standard procedure essential to collect blood samples for clinical use.
In premature babies, a response to the heel lance of non-specific neuronal bursts -- general bursts of electrical activity in the brain - was recorded.
After 35-37 weeks, the babies` response changed to localised activity in specific areas of the brain, indicating they were now perceiving painful stimulation as separate from touch.