Neural scans involving 28 first-time mothers show that when a woman looks at a photo of her baby smiling the reward centres of her brain light up.

These regions, called the substantia nigra, the striatum and the frontal lobe, are involved in emotion processing, cognition and behavioural outputs.

Lead researcher Lane Strathearn, a Queenslander now based in the United States, said these areas had also been activated in experiments associated with drug addiction.

''It may be that seeing your own baby's face is like a natural high,'' Dr Strathearn, who is now based at the Baylor College of Medicine in Texas, said.

The study, published in the journal Paediatrics, showed this maternal activation was strongest with smiling faces. Photos of babies crying did not evoke the same brain response.

In fact, there was little difference in mothers' brains when they saw their own baby's crying face compared with that of an unknown child, Dr Strathearn said. AAP