Life’s milestones, from walking down the aisle at graduation to walking down the aisle at our wedding, are among the happiest times of our life that may be inexplicably filled with tears — specifically tears of joy. Crying, in essence, is a good way for us to release sadness, stress, and toxins, but what about when we’re filled with joy? The phrase “I’m so happy I could cry” actually makes sense, according to a recent study to be published in a forthcoming issue of Psychological Science, which found we restore our emotional balance by responding to positive experiences with negative emotions.

"People may be restoring emotional equilibrium with these expressions," said Oriana Aragon, lead author of the study and psychologist from Yale University, in a press release. "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."

Aragon became inspired to examine these "dimorphous expressions" of positive emotions, as she calls it, after hearing Leslie Bibb describe this impulse to Conan O’Brien, The Washington Post reported. These two odd responses stem from the very same emotion.

Aragon and her colleagues at Yale University sought to examine people’s emotional responses to different scenarios by conducting a series of two studies. In the first study, 143 participants were recruited and asked to answer whether they cry when seeing loved ones reunited or while watching the happiest moments of movies, and whether when holding a cute baby if they have "the urge to squeeze his or her little fat legs.” The researchers observed the negative and aggressive responses to positive emotions.

The findings revealed people who had negative or aggressive responses in one scenario were likely to have them in another. For example, the participants who cried at their kid’s graduation were more likely to have the urge to pinch a baby’s cheeks. Aragon suspects these reactions take place "when people are overwhelmed with emotions.”

In a different study, Aragon and her research team recruited about 300 participants to show pictures of babies, which were altered to make them look more or less cute. Immediately after viewing those photos, the researchers measured people’s feelings and repeated this again five minutes later. Cuter babies were viewed more positively and yielded responses such as, "I want to pinch those cheeks!" or telling the baby, through gritted teeth, "I want to eat you up!"

Overall, people who had aggressive or negative reactions to positive emotions were found to recover better from their emotional highs and were closer to attaining emotional equilibrium than people who had no interest in, for example, pinching baby’s cheeks. This suggests negative reactions, such as tears of joy, may help people calm down when they’re overwhelmed with joy.

"It took me a long time, a lot of experiments, and a lot of work, to say: yes, people are actually feeling positive [emotions] but expressing negative [responses], and do so across a variety of situations," Aragon said, The Washington Post reported. She went on to say, "We really want emotional homeostasis. We want a happy, middle spot. Extreme is not good. It's hard on our bodies."

The reverse can also be true: Strong negative emotions can also elicit positive expressions. For example, we tend to go into nervous laughter when confronted with uncomfortable situations. In the most famous Stanley Milgram’s “Milgram experiment,” the researcher set out to discover why some people will blindly follow authority. Test subjects were asked to deliver a series of increasing powerful electric shocks to the unseen person, “the learner” (who were Milgram’s team members playing a role) to observe how much voltage they would deliver before they refused to continue.

While an astounding 65 percent delivered the experiment’s final jolt of 450 volts, more shockingly, Milgram noted the subject began to laugh nervously once they heard screams of pain coming from the unseen “learners.” This suggests humor could be a defense mechanism we use to guard ourselves against overwhelming negative emotions. It’s a way to cope with heightened emotions and restore our emotional balance.

The scientists based their findings on the belief that people have emotional limits. If our sadness or joy is reaching an unmanageable limit, our bodies therefore become physiologically overwhelmed. This triggers the unexpected emotion — like tears of joy — to reach emotional equilibrium.

Ironically, these unusual “embarrassing” displays help with our self-regulation.

Source: Aragon O, Bargh JA, Clark MS, Dyer RL. Why 'I'm so happy I could cry' makes sense. Forthcoming Psychological Science. 2014.