Dear Science - The Stranger

Dear Science,

Many years ago when I was in college, I used to do push-ups in my dormitory room. A couple of times, my roommate decided to crack jokes about me in the middle of my set, and invariably I would start laughing, suddenly lose all of the strength in my extremities, and crumple up into a limp mass on the floor. Recently I was exercising at home, and my wife made me chuckle while I was in the middle of a set of pull-ups; once again, I found myself drained of all strength and unable to move an inch toward the bar. So my question is: Why does laughter drain the strength from my body for several seconds and make me as weak as Superman after a kryptonite enema? Does everyone suffer the same kind of reaction? Does this have to do with laughter being a kind of convulsion or something?

Laughter = Kryptonite

Yup, it happens to everyone. Get prepared for a word that'll change your life, for the better or worse: cataplexy, the sudden physical collapse caused by experiencing strong emotions or laughter. Why? Now that's a tougher question.

Feeling weak from laughter appears to be from the temporary inhibition of the motor neurons—the cellular wires that connect your brain to your muscles—around the body. How do we know this? By testing a leg reflex—otherwise known as the H-reflex—when showing volunteers movies. Start to laugh, and the reflex goes away. Seeing something funny isn't enough; one must actually laugh to bring on the feebleness.

Okay, but why? Two explanations compete for your acceptance. One says that any really deep breath out causes weakness; a big exhalation alone can cause the same poor H-reflex. Perhaps the incapacity is just from breathing out a whole bunch of air at once. The alternative theory lays the blame at the emotion of mirth, which is accused of sending the spinal cord into a fit of paralyzing activity. Can deep amusement itself cause the weakness, independent of the effects on breathing?

Time for a truly awesome study to figure it all out. The dream team of Overeem, Taal, Gezici, Lammers, and van Dijk assembled. Twice a second, the H-reflex was measured. Volunteers did 10 different tasks, including sitting quietly, coughing, faking laughter, and "true" laughter, caused by scientists telling jokes. "True laughter was obtained in all participants," the team noted defensively. "There are probably two reasons for this high success rate. First, we did our best to create a relaxed atmosphere conducive to laughter. Second, using a large stimulating surface electrode... helped to reduce the pain" of forcing the reflex.

The result? Faked laugher (with a similar effect on breathing as real laugher) had a much weaker effect than the real thing. The conclusion? The crazy breathing pattern contributes, but mirth wins the kryptonite crown.

Gleefully Yours,

Science

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