London: Babies as young as three months old can distinguish sad from neutral sounding voices even when they are asleep, British scientists have found.

The findings, the researchers said, have implications for future research into how brain function and development relates to later disorders such as autism.

"It is probably because the human voice is such an important social cue that the brain shows an early specialisation for its processing," said Anna Blasi, study researcher from Kings College London.

"This may represent the very first step in social interactions and language learning," Blasi said.

For the study, published online in the journal Current Biology, the researchers scanned the brains of babies between 3 months and 7 months while they were asleep.

They played neutral humans sounds, such as coughing or yawning, and compared the babies' brain reactions with those produced when the babies heard sounds of water or toys.

The part of the brain that in adults reacts to human vocalizations lit up when the researchers played the neutral human sounds, the researchers said in a statement.

"We were very surprised to find that the area of the temporal cortex that responded to the human voice more than to environmental sounds was so similar in its location to the adult area showing the same specialization," Evelyne Mercure of University College London said.

When the babies heard sad sounds such as crying, there was an increase in activity in the regions linked to emotional processing in adults, which could mean babies are already able to empathise and understand different emotional states.

"We are now carrying out more research in this area to help us understand how differences in brain development arise, and if we can use these to accurately identify babies who will go on to suffer from disorders such as autism," study author Declan Murphy, of King's College London, added.

(Agencies)