Hitting a Nerve

Circadian curiosities


Summer is here. Well, technically not for 3 weeks, but in Phoenix summer as a weather condition generally runs from March to November.

The suprachiasmatic nucleus (yes, the one you learned in neuroanatomy) is pretty tiny, but still remarkable. Nothing brings that into focus like the changing of the seasons.

No matter where you live on Earth, you still have to deal with day and night, even if each is 6 months long. We all have to live with shifting schedules and lengths of night and day and weekdays and weekends.

Dr. Allan M. Block, a neurologist in Scottsdale, Ariz.

Dr. Allan M. Block

But what fascinates me is how the internal clock reprograms itself, and then doesn’t change.

Case in point: Except for when I’ve had to catch a flight, I haven’t set an alarm in almost 10 years. Somewhere early in my career (back when I did a lot of hospital work) I began getting up between 4-5 a.m. to start rounds before going to the office.

Today the habit continues. It’s been 14 years since I last did weekday hospital call but I still automatically wake up, ready to go, between 4 a.m. and 5 a.m., Monday through Friday. Without me having to do anything this shuts off on vacations, holidays, and weekends, but is up and running as soon as I have to go back to the office.

It’s fascinating (at least to me) in that the suprachiasmatic nucleus didn’t evolve many millions of years ago so I could get to work without an alarm clock. Early animals needed to respond to changing conditions of night, day, and shifting seasons. Light and dark are universal for almost everything that walks, flies, and swims, so given enough time a way of internally keeping track of them developed. Bears use it to hibernate. Birds to migrate with the seasons.

Of course, it’s not all good. In some people it’s likely behind the bizarre predictability of their cluster headaches.

In the modern era we’ve also found ways to confuse it, with the invention of time zones and air travel. Anyone who’s made the leap across several time zones has had to adjust. It’s certainly not a major issue, but does take some getting used to.

But still, it’s pretty fascinating stuff. A reminder that, for all we do in our every day lives, the brain does things on autopilot that we don’t even think about.

Dr. Block has a solo neurology practice in Scottsdale, Ariz.

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