这貌似是一个奇怪的反应：当你高兴的时候会流泪。不过，一些心理学家称，他们发现了其中的原因，喜极而泣很有可能是身体恢复“情感平衡”的方式。

It may seem like a strange response: to break down in tears when you are happy.

But now a group of psychologists say they have found the reason why, and that crying tears of joy may well be the body's way of restoring "emotional equilibrium".

The psychologists say that, by responding to an overwhelmingly positive emotion with a negative one, people are able to recover better from strong emotions.

Oriana Aragon, the lead author of the report which will be published in the journal Psychological Science,said: "People may be restoring emotional equilibrium with these expressions.

"They seem to take place when people are overwhelmed with strong positive emotions, and people who do this seem to recover better from those strong emotions."

The psychologists from Yale University examined subjects' emotional responses to different scenarios, including happy reunions and "cute" babies.

They found individuals who expressed negative reactions to positive news were able to moderate their intense emotions more quickly.

They also found people who are most likely to cry at their child's graduation are also most likely to want to pinch a cute baby's cheeks.

They cited other examples of where people responded to a positive experience with a negative emotion, including concert goers screaming in horror at the presence of their idol and lottery winners breaking down in tears.

The report authors said: "To give an example, upon winning the lottery, one might appraise the event as an incredibly good thing; feel overwhelmed with happiness, smile and cry.

"One's appraisal that winning is a good thing, intense happiness and verbal expression would easily be described as positive, yet there is also an expression of crying which normatively expresses sadness.

"This expression is not inherent to the situation, the appraisal, or the positive emotions. The negative expression might be merely a facial display, or it might reflect actual negative emotions."