Only when I laugh: the science of laughter


The human voice is the most complex instrument in nature. When we talk, we shape sounds in the way no other animal can. This reflects the very precise evolutionary adaptation that means, for example, our tongues are short and fat and nimble, rather than long and hard to maneuver. It also reflects the very fine voluntary motor control that we have over our mouth and our rib cage, which enables us to control the act of talking, and also the fact that unlike many other animals, we learn new patterns of vocal behaviour. And of course, this is only the start of our abilities – we can do vocal impressions, sing, beatbox – when it comes to the human voice, the sheer range of abilities is extraordinary. However, these voluntary motor acts can be derailed quite efficiently by a different vocal behaviour – laughter.Allow content provided by a third party?

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This means that when people start to laugh hard, they start to make sounds that we never normally hear in any other context – when I laugh hard, the pitch of my voice goes much higher than my speech. And if we are speaking, or trying to speak, the effect of the laughter will be immediately apparent, as we start to lose control over the muscles in our rib cage, that normally work with such precision during speech.

There are some very famous recorded examples of this loss of control – for example Brian Johnston and Jonathan Agnew, doing a piece on live radio discussing that day’s cricket, and getting completely hijacked by laughter. Agnew makes a terrible joke about Ian Botham not quite getting his ‘leg over’, and starts to laugh: Johnston keeps talking but the pitch of his voice has already been affected – although he is not yet laughing, his voice control has altered. After a few seconds further talking, during which he asks Agnew to stop laughing (Aggers, do stop it!), Johnson finally succumbs to the laughter and the pitch of his voice soars, and he becomes unable to actually speak. Agnew tries to take over, and fails completely; Johnson completes to the report “He hit a four over the wing keeper’s head” at an incredibly high pitch, and the starts to get the control of his voice back “England were all out for 419, I’ve stopped laughing now”. You can actually see the pitch of his voice subsiding as Johnston gets control back over his speech (I made a very short video about the acoustics of their laughter here).

But the really striking thing is that they were laughing at all. These were broadcasting professionals, and they were not supposed to laugh while on air – but they still did. And we have all had that experience of finding ourselves starting to laugh, sometimes in terribly inappropriate situations. A really powerful effect of laughter is that if we start to laugh it can be excessively difficult to not go through with the laughter – it will come out one way or the other. And when we do start to laugh, it stops us breathing, and it stops us talking, and it just squeezes air out of us – effectively, laughter is trying to kill us.

We are making big developments in understanding the perception of laughter, but I’m also really interested to know more about why we can be overwhelmed by laughter in this way – what is the brain basis for this? A study from Germany has found differences in the hypothalamus when people are laughing because they are tickled as opposed to forcing themselves to laugh – but are there any other differences? Why, for example, do we become weak and floppy when we start to laugh? The evidence suggests that this only happens when we are laughing hard – polite social laughter doesn’t render us helpless. It’s the emotion, which is incapacitating us, not just the action, and I would really like to know why.