Your Brain is a Time Machine: The Neuroscience and Physics of Time

by Dean Buonomano

Anyone who has endured the mental and physical haziness of transmeridian travel can attest to the challenges of resetting our circadian clocks. It can take days to resynch the suprachiasmatic nucleus after a trip between Los Angeles and London—the rule of thumb is up to a day for each hour your circadian clock has to be advanced. In contrast, the clocks on our wrists can be instantly reset to match the local time zone. This difference reflects the distinct design principles of man-made versus circadian clocks. The oscillation frequency of the quartz crystal of most wristwatches is 32,768 Hz, so an hour simply consists of counting 32,768 x 60 x 60 of these ticks. Resetting your watch upon arriving in London does not require tinkering with the oscillator itself, but simply changing the current total tick count by advancing the hour hand (or digit)—a mere formality. In sharp contrast, the pendulum of the circadian clock requires a full day for a single swing, so resetting it requires the much more delicate task of mucking with the actual oscillator, akin to advancing a pendulum in mid-swing. The “swing,” in this case, refers to the rise and fall of the circadian proteins within our cells. It is simply not possible to instantly reset the concentration of the circadian proteins within a cell, any more than it is possible to instantly reset an hourglass that is half full.