• Home
• /
• Opinion

How a clock in your brain rules your life

Imagine looking at a slow-motion film, taken from above your town. It records what happens over several days. You run the film: it's easy to see waves of activity: a rush of traffic in the morning, a surge of pedestrians around midday, a second flood of traffic in the early evening. You also notice that the lights go on in the early morning, and go off again in the late evening. You're watching the rhythm of life: your life. And that of most other people. What you may not know is that this rhythm isn't spontaneous, or regulated by habit or work, but by a tiny clock in your brain.
The clock is a collection of nerve cells, called the suprachiasmatic nucleus, an impossibly long name that always shortened (even by neuroscientists) to SCN. It's a true clock, because it ticks away all by itself (energy provided by its blood supply - like the clockwork or battery in your watch). But it can't tell the time, and like your watch, has to be set to enable your rhythm to match those of others and the external world. It's connected to your eyes, and special sensors tell it when the lights come on (the sun rises) and when they go off (sunset), so it's synchronised to daylength. If you put someone in a dimly lit (red light) cave for several weeks, then the SCN clock reverts to its natural rhythm. The fascinating result is that each of us has a slightly different rhythm: yours might be 24.6 hours, mine 23.8, and so on (it's never too far from 24). If you were asked to keep a count of the number of days you had spent in the cave then you would underestimate the time, because each of your 'days' is now longer then it should be: I would do the opposite. But we would both revert to the same 24 hour rhythm when we returned to the normal world with its 24 hour day. This is why, despite these differences in the ticking of our SCN clock in the cave, in real life we are all (more or less) synchronised with each other.
But these differences don't disappear altogether, even in the everyday world. You may be an 'evening' person (an owl): I may be morning one (a lark). That's because your SCN clock finds it more difficult to reduce it's natural rhythm to 24 hours from 24.6 (or whatever) whereas mine finds it easier. So your 'peak' of SCN rhythm may be later. Interestingly, during adolescence the SCN clock tends to delay its peak, which may be why young people have such a problem getting out of bed in the morning! 
How does this tiny part of the brain work? Not like the watch on your wrist, whether it's a clockwork or electronic one (they are quite different as well, but that's another story). Each day, there is a rhythmic surge of a number of proteins in the SCN: these regulate the signal it gives to the rest of the brain, and indeed, to the body.
The formation of these proteins is, in turn, regulated by a number of genes. The rhythm occurs because as the amount of protein increases, it does two things: signals the time of day, but also suppresses its own formation by acting on the gene that makes it. So the concentration of protein falls, but as it does so, it liberates the gene. You can see how this will result in an oscillation that will be rhythmic. Genes are not exactly all the same in all of us (mutations), which accounts for why your rhythm may differ from mine. But in both of us our behaviour is driven by our SCN, itself modulated by light, and so the world moves in synchrony, and there's a daily rush hour.
Under more normal conditions shift work will disturb rhythms, including cortisol.
The SCN clock has constantly to reset itself as people move onto, and off, night shifts. There is a huge literature on the consequences of shift work for health, and methods have been developed for making transitions from one environment to another as easy and non-damaging as possible. Aircraft crews are another instance of frequent changes in time zone. No one has really shown that this is damaging, but airlines take precautions about the number and rate of time zones to which their staff are exposed.
Remember, next time you sit in that traffic jam, that it's just a little bunch of nerve cells in the brain that drives the rhythm of the life that you, and everyone else, lives. -Psychology Today 
Joe Herbert is an emeritus professor of neuroscience and former chair of the Graduate School of Biosciences at the University of Cambridge.