New York, July 16 (IANS): Sleep deprivation hampers our ability to accurately read facial expressions and can put us at various risks in daily life, shows a study.

Sleep deficit can have serious consequences such as not noticing that a child is sick or in pain or that a potential mugger or violent predator is approaching.

"Recognising the emotional expressions of someone else changes everything about whether or not you decide to interact with them and, in return, whether they interact with you," said study senior author Matthew Walker, professor of psychology and neuroscience at University of California-Berkeley.

The results do not bode well for countless sleep-starved groups.

"Consider the implications for students pulling all-nighters, emergency-room medical staff, military fighters in war zones and police officers on graveyard shifts," said Andrea Goldstein-Piekarski, postdoctoral fellow at Stanford University in a paper published in the Journal of Neuroscience.

For the experiment, 18 healthy young adults viewed 70 facial expressions that ranged from friendly to threatening -- once after a full night of sleep and once after 24 hours of being awake.

Brain scans revealed that the sleep-deprived brains could not distinguish between threatening and friendly faces.

Additionally, the heart rates of sleep-deprived study participants did not respond normally to threatening or friendly facial expressions.

Moreover, researchers found a disconnection in the neural link between the brain and heart that typically enables the body to sense distress signals.

This may explain why people who report getting too little sleep are less social and more lonely.

"Sleep appears to reset our emotional compass. This study provides yet more proof of our essential need for sleep," the authors said.