The Nocturnal Brain summary

If you’ve ever been jet-lagged after a holiday, you can imagine how grim it must feel to be permanently out of sync with the world. 

For 16-year-old London schoolboy Vincent, this out-of-sync sensation was a permanent, 24-7 reality. His problems started gradually. He found it more and more difficult to get to sleep, and would eventually drift off at 3 a.m. Soon, Vincent would want to sleep at 11 a.m., and wake in the evening. He struggled to attend school, and his mother, Dahlia, felt judged for her son’s poor attendance record. Two years and countless medical examinations later, the cause of Vincent’s problems was finally identified. His body clock was running on a 25, rather than 24-hour cycle, putting him completely out of sync with the world around him. 

All life on earth runs on a natural 24-hour cycle called the circadian rhythm, that keeps us broadly in line with the movements of the sun. When it comes to sleep our rhythm is influenced by the production of a hormone called melatonin. Melatonin guides our brain in and out of sleep. If your sleep pattern is normal, your melatonin levels increase in the early evening, stay high in the night, and then drop in the early morning. 

However, our melatonin production and circadian rhythm can be disrupted. Exposure to bright light in the evening, for example, will suppress melatonin levels, and with it, your natural ability to get to sleep. That’s why lying in bed, bathing in the bright blue light of your smartphone screen is such a bad idea. 

More seriously perhaps, there is evidence that people working night shifts, and who fight against their natural circadian rhythm, suffer serious consequences. A 1996 Norwegian study found higher levels of breast cancer amongst radio and telegraph operators who worked irregular shifts, and this finding has been replicated elsewhere. The World Health Organization has even listed ‘circadian disruption’ as a possible cause of cancer. 

But, as poor Vincent found out, a disrupted circadian rhythm means a disrupted life. Thanks to his 25-hour cycle, Vincent’s body wanted to sleep one hour later every day. As a result, he was regularly exhausted at 2 p.m., or totally alert at 1 a.m. His school suffered, and so did his social life, as his irregular sleeping got in the way of meeting friends. 

And in that sense, Vincent’s experience points to another, unexpected function of our circadian rhythm.  It is crucial to our sense of self as humans. To be awake deep into the night, while the world around you sleeps, is a profoundly lonely experience. We humans are social beings. Although our circadian rhythms evolved to keep us in line with the rhythms of the sun, they have an important side effect; they keep us synchronized as a society.