If you think your crying baby calms down when you pick him or her up is because of the warm embrace of your loving arms, think again: there is a more scientific reason.
In fact, what happens is that their heart rate slows and they 'automatically and deeply' relax.
Japanese scientists say their study is the first to demonstrate that a baby's response to being carried is a coordinated set of nervous, motor and cardiac regulations.
The researchers, from the RIKEN Brain Science Institute, say that picking up and carrying might be an evolutionarily, and essential, component of mother-baby interaction.
In experiments involving ECG machines, which measure electrical activity of the heart, they found that babies' heart rates slow down greatly as soon as they are picked up and carried.
Using a very small ECG system, they were also able to observe the same phenomenon in mice.
Both human and mouse babies calm down and stop moving immediately after they are carried, and mouse pups stop emitting ultrasonic cries. But the calming effect doesn't happen when babies are simply held.
"This infant response reduces maternal burden of carrying and is beneficial for both the mother and the infant," explained one of the study authors, Dr Kumi Kuroda, in the journal Current Biology.
"Such proper understanding of infants would reduce frustration of parents and be beneficial, because unsoothable crying is major risk factor for child abuse.
"Although our study was done on mothers, we believe that this is not specific to them and [the findings] could be applied to any primary caregiver."