They may be hungry, tired - or just need their nappy changed. But whatever distresses a tearful baby their cries are impossible to ignore.

Research by Dublin-born scientist Christine Parsons has shown why we respond so swiftly to a baby's cries compared to the tears of an adult.

It's all due to activity in the reward region of the brain, known as the orbitofrontal cortex, said Professor Parsons.

Adults' brains light up to the sound of a crying baby in around 130 milliseconds, said the Maynooth graduate.

Ms Parsons, who is now associate professor of Aarhus University, Denmark, said the research was particularly valuable in understanding what a normal response is.

The findings help shed light on post-natal depression - where mothers struggle to bond with their newborn - by showing how a healthy brain responds to a baby's cries.

"Our work has used a range of brain imaging methods to understand human behaviour, motivation and emotion processes," Prof Parsons said.

"This research is fundamental to our understanding of the parental brain - it shows how the brain is geared to respond to a baby's cry.

"A baby's cry has built-in features that make it difficult to ignore.

"We think the way that adults respond to these important signals from babies can have long-term effects on development."

Prof Parsons, who will deliver an Alumni lecture this evening at 7.30pm as part of Maynooth University Science Week, pointed out that around 14pc of women in developed countries suffer post-natal depression.