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June 22, 2016

Infrequently Asked Questions: Why do we cry when we laugh?

Even if we haven't experienced it ourselves, we've certainly all witnessed a friend, family member or audience cohort at Helium start weeping after a gut laugh. But it's not exactly obvious why that is — one would think those tears are reserved for "Bambi" viewings and deaths in the family, after all.

So, why are we crying when we're so happy? 

We reached out to Dr. Joan O'Brien, chair of the University of Pennsylvania Scheie Eye Institute, for an answer.

Why is it that some of us cry when we have a really hard laugh?

So, some people speculate that both are cathartic experiences — they even look alike. And they’re related in the brain in a way that — most comedy relates embarrassing or sad events in a way that causes humor and laughter. So the question is whether this combination of laughter with tears is centrally modulated or more locally modulated. And there’s data to suggest both. In his book ['Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond'], Robert R. Provine speculates that both laughter and crying results in a feeling of catharsis. And that they may emanate from the same center, and he speculates they lure stress hormones such as cortisol and adrenaline. And the data for that is really just in his book. 

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Others have speculated that when you laugh really hard, you squeeze your eyes shut. And when you squeeze your eyes shut, you have something called reflex tearing, which is usually caused by wind or foreign bodies. But in the setting of enough squeezing, it may have a local effect. Dr. William Frey, from Minnesota, who authored ‘Crying: The Mystery of Tears,’ he found that emotional tears contain a greater concentration of protein than tears produced in other ways. And Frey speculated in that article that tears result in the situation of sadness by removing harmful substances produced by stress. So, in that way, she agrees with Robert Provine, who speculates that they’re coming from some point of catharsis and releasing of stress.

There are different kinds of tears?

There's a normal tear film that covers your eye and your cornea which is necessary to keep your cornea protected. But reflex tears, they come from your lacrimal gland and they are trigged by some kind of stimulant. So, dry eye can cause tearing, believe it or not; and wind, which causes drying, can cause tearing. And so it may be that squeezing your eyes tightly could cause reflex tearing as well.

So the common thread might be cortisol?

And adrenaline. They are stress hormones. But whether anyone has ever measured them, I did not find. It would be very hard to measure in a setting of a laugh with crying. It just doesn’t happen. So that’s really speculation.

There is also a central nervous system problem that causes people to have pathologic laughter and crying syndrome. And so that’s an illness in the brain that is characterized by uncontrollable outbursts of both crying and laughing. And these patients with PBC have damaged pathways in the motor areas of their brain and it goes all the way down to the brain stem. And this suggests there's a common area of laughing and crying which can be damaged, resulting in inappropriate control mechanisms for both.

I've witnessed people not just tearing up when laughing, but sobbing — one emotion transforms into another. Happy laughter to miserable sobfest. What's the deal there?

And I think the opposite happens as well. You see people at funerals who are stressed who are crying and then start laughing. I mean, that’s something I’ve observed not infrequently. And that suggests that there is some — that, [in addition to] the presence of a disease related to damage in the brain, suggests there may be a central component to this.

But still more studying to be done?

I wasn’t convinced that there was true medical knowledge of this. It’s hard to imagine how exactly you would study it. You can’t have an animal model that laughs and cries. You could study in people, but you’d have to be there when they do that and they don’t do that a lot. So to have real knowledge, you could look at a functional MRI of the brain and see what areas light up when laughing and crying — maybe that could be done. But it would take a lot to get someone triggered to cry in an artificial setting and even to laugh. Maybe you could and we have the means to look at the brain that way, but looking at the literature, I didn’t see that.

Anything to add?

When people laugh and cry they often look the same. Sometimes you think someone is laughing or crying and they’re doing the opposite. So the fact that your facial expression triggers can be similar, and that there’s this [neurologic condition], related to damage in the brain, that to me suggests there may be a central component, as well as perhaps a local component.

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