Suzana Herculano-Houzel

Column_117 Jetlag

Ah, the problems of modern life. When we were only bipeds and had no artificial light, going to sleep and waking up were simple matters, dictated by the time of the sun (and disturbed at most by an evening fire, or later a lamp); it was impossible to change time zones in the space of a day when you only walked. Then came transatlantic ship journeys, when solar time changed – but slowly, over several days.

And then… we invented the airplane, and with it the rapid movement between meridians on the planet. For example, last night I was at home in Rio de Janeiro, and today I’m already in California, more than 9,000 km away and five meridians to the west, plus our daylight saving time. The result: it’s eleven in the morning here, but my brain thinks it’s five in the afternoon and my lunch is more than late. I lie: I “ate lunch” at 8 a.m. in Texas, when for me it was already noon, but now it’s time for lunch again. Or is it “dinner”?

The fact that we suffer from jetlag is proof that our lives, although they follow solar time, are not dictated by it – otherwise we would go to sleep when the sun goes down, whatever the time, and wake up peacefully at local dawn. The mismatch with the change of time zone is a sign that we have an internal brain clock that regulates our schedules: a real pacemaker, located just above the point where the optic nerves enter the brain. An ideal place, by the way, for a structure that is informed by the eyes about the ambient light, which tells the brain whether it is day or night.

Even if we were to stay in absolute darkness for days, we would maintain our sleep and wake times, but with a rhythm of around 25 or 26 hours, not 24. It is this characteristic of the internal clock that allows us to adapt to a new time zone: every day, the internal clock, which is longer than the solar day, is adjusted to the local time depending on when the ambient light increases – for example, when we leave the house and expose ourselves to the sun.

Going out in the sun in the new time zone is therefore the best recommendation for adjusting to local time straight away. So I’m going to hold out until a reasonable time to fall asleep here, maybe around nine, and hope that tiredness keeps me in bed until at least 5am. But flying west is easy; it’s getting home that’s going to be tricky…

Originally published on November 2011, on Folha de São Paulo

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