Have ever wonder why newborn babies cry when they come out of mother's womb? It is obvious for a new mother to feel extremely happy to hear her child's voice but the reason behind it is not that joyous. According to a new study due to stress and pain, babies start crying when they are unable to express their real feelings.

Researchers have found that a newborn baby's brain shows a heightened response to pain which they express through crying. Sometimes stressed babies brain might not respond to the pain. But many times the caregivers underestimate the baby's pain experience. In this case, researchers have suggested that it is extremely important to identify different ways to understand their stress level.

"When newborn babies experience a painful procedure, there is a reasonably well-coordinated increase in their brain activity and their behavioural responses, such as crying and grimacing," said Laura Jones from the University College London as quoted by IANS.

"Babies who are stressed have a larger response in the brain following a painful procedure. But, for these babies, this greater brain activity is no longer matched by their behaviour," Jones further added.

The study was published in a journal Current Biology. The research team did an experiment on newborn babies where they enrolled healthy infants, boys and girls from the postnatal ward and special care baby unit. The experimenters measured those babies' stress level based on salivary levels of cortisol, which is a steroid hormone and their heartbeat patterns. At the same time, researchers also used electrophysiological monitoring method called EEF to record their brain activity and facial expression.

The outcome of the process has revealed that babies with higher levels of background stress showed a bigger brain reaction to the heel lance procedure, which is a standard way of taking blood samples from newborn babies. However, that heightened activity in the brain didn't correspond to a change in the babies' behaviour.

On the other hand, Jones said that the study on newborn babies has also suggested taking care of babies in such a way, which will help them to release the stress and pain.