It’s always easy to get caught up in computational work, so let me describe a quick experiment you can do to relieve the boredom. Sit down in your spinny chair and cross your legs. (You do have a spinny chair, right? If not, get one – they prevent repetitive strain injuries, and more importantly, they are great fun. This experiment works best if the chair has no arms.) Start spinning that spinny chair until you feel like you’ve achieved a stable rotation. Then – smartly – stop the rotation and sit up straight.
This experiment is best done with a partner who can watch and laugh. Done right, you careen to one side as you do your best to push yourself upward. You find the the room is rotating around your shoulders while you lean dangerously to one side and seem to be tumbling back.
I did this on James, my esteemed colleague – there was some question about whether I did it ‘with’, ‘to’, or ‘on’ him – and his reaction, like that of many who undertake this test, is that it is profoundly disorienting. The first few times I did it, I rapidly felt profoundly nauseous, and even though I knew what was coming, I swung myself left as I tried to sit up. Changing the whether or not you keep your eyes open and whether or not you continue spinning after sitting up can make it more or less nauseogenic.
Motion sickness is an innate response to confused motion sensations. Your motion sensors aren’t built for spinny chairs and aeroplanes. You sense acceleration, only above a threshold minimum, and you only correctly identify motions when you are rotating in a narrow window of terrestrial possibilities.
Why – why – do our bodies do this? Why would evolution, which has given us the most powerful brain in the animal kingdom, powerful enough to build machines that throw our bodies around like beanbags, not rid it of this bizarre and incapacitating phenomenon?
I did an experiment. For years, I have avoided a particular kind of shellfish. Mussels, on several previous occasions, been linked to vomiting for me. After ten years of avoidance, I decided it was time to try them again. I sat down at a restaurant and ordered a full plate.
It was all quiet for about two hours. And then – just as I was about to declare victory over my suspected allergy – a twinge of nausea hit me. I sat down and started breathing to control it. But this, now, was my opportunity. I stood up, closed my eyes firmly, lifted one foot off the ground, and began to count.
Of course this experiment is imprecise. My rate of counting may not be consistent, and there is a significant placebo effect associated with knowing what the experiment is. But nonetheless: I really, genuinely struggled to get more than 25 seconds of standing on one foot. I just couldn’t keep myself upright.
Our best guess is that motion sickness solves a real problem for early humans: detecting when food was good and bad. Bad food – neurotoxic food – causes your nerves to send the wrong signals. Or it causes your nerves to send the right signals at the wrong times. Evolution’s best solution has been to link this to your sense of balance, a precisely coordinated set of neural signals. These signals have to come at the right time. If you get the timing even slightly wrong, your brain senses the wrong orientation.
When your visual picture of the motion and your inference about the motion conflict, you assume – unconsciously, unprompted, and irrationally – that the cause is a neurotoxin in your system. Your brain tells you to throw up. You do.
The mussels stayed down, fortunately, but my experiment was consistent with the idea that there was a problem with my motion sensing while I was unwell. Even more powerfully, lab animals without a functioning vestibular – motion-sensing – system do not respond to the usual range of emetic drugs.
The story of motion sickness is one of a peculiar interaction between evolution, anatomy, and modern life. Knowing more about it can help you cope and adapt. It’s annoying, but it’s also fascinating.
