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.

It has long been hypothesized that the phases of the moon play a role in human physiology. For example, as the term lunacy suggests, it was believed that the full moon could cause people to go insane; contemporary scholars think this association arose because changes in sleep patterns triggered by the light of the full moon may have pushed people suffering from epilepsy or bipolar disorder over the edge. Additionally, the fact that the human menstrual cycle is very close to the lunar month hints at a role for the moon in human reproduction. This appears to be a mere coincidence, as the menstrual cycle of other primates can be significantly shorter or longer. So, other than the obvious fact that lunar light could alter sleep and social activities, there is little evidence that the phases of the moon have any direct impact on human physiology.25

Prospective timing is a true temporal task in that it relies on the brain’s timing circuits. In contrast, retrospective timing is in a sense not a timing task at all; it is rather an attempt to infer the passage of time by reconstructing events stored in memory. The distinction between prospective and retrospective timing explains a few of the mysteries about our subjective sense of time, including what some have called the holiday paradox.5 A five-hour wait for a delayed plane on your vacation trip to Greece can seem endless as it is unfolding, while an exciting day touring Athens flies by. A week later, however, the airport delay is a mere blip in time, while the busy, fun-filled day in Athens seems quite extended.

Such deficits led to fundamental insights into how the brain stores memories. So it is natural to also ask if specific disorders abolish people’s ability to tell time on the scale of around a second. The answer is no. There are no known neurological conditions that result in people losing their ability to appreciate the rhythm of music, and reproduce intervals in the range of seconds, and learn to blink at the right time in response to a tone. Nor should we expect there to be because different temporal problems are solved by different circuits within the brain.

Perhaps you have encountered the dilemma of being told that next Wednesday’s meeting has been moved forward two days. So do you show up for the meeting on Monday or Friday? “Forward” is generally taken to be in the direction of movement. Thus if you are moving through a static timeline, and the timeline is moved forward, the target day will put it farther away, on Friday. But if you are standing still, and we conceptualize time itself to be flowing by you, putting the meeting forward will place it closer to you, on Monday. The first interpretation (Friday) is described as an ego-moving perspective, and the second (Monday) as a time-moving perspective

Different people and cultures vary dramatically in how much thought and effort they apply towards the future, and how far ahead they mentally travel into the future. We all know people who, a bit like the Pirahã, seem to live day by day—they are the ones who generally appear to be content, despite seeming to run into more than their share of financial and personal difficulties. At the other end of the spectrum are those whose every thought and action is aimed at achieving some goal in the distant future.14 And then there are the visionaries who dream decades and centuries into the future. This ability to time-travel beyond the lifespan of any individual is perhaps the cornerstone of human culture.

The truth is that even though humans are far better at long-term planning than all other animals, we are not particularly good at it. This should not come as a surprise. The human brain is the product of an evolutionary process that unfolded over hundreds of millions of years. So most of our neural baggage comes from animals that lived, cognitively speaking, in the immediate present. Consequently, as a species, humans are still learning to perfect our newly acquired skills to better balance the allure of immediate gratification with the benefits of delayed gratification.

As mentioned previously, mental time travel is both a gift and a curse. Our trips to the future generally take us to places that we deem to be superior to our current circumstances, and often serve to outright escape the present. But as emphasized in Eastern philosophies, traveling to the past or future can preclude us from embracing the here and now as a primary source of happiness and joy.33 Daniel Everett alludes to this: “The Pirahã simply make the immediate their focus of concentration, and thereby, at a single stroke, they eliminate huge sources of worry, fear, and despair that plague so many of us in Western societies.” But if living in the present provides a more carefree life, it also provides much less of it (the Pirahã’s average life span is around forty-five years, not taking into account infant mortality).34 Ensuring a continuous supply of food, providing permanent shelter, engaging in scientific and artistic endeavors, and preventing and curing diseases all require vast amounts of foresight and planning. And therein lies the paradox of mental time travel: it seems to be both the solution and the cause of all our troubles.