Body clock maths: staying human in the age of technology

What does it take to push the human body clock to the limit? Technology marches on and some clever maths can help to establish the boundaries.
6 September 2023

Circadian rhythms: the human body clock does it’s best to keep our waking and sleeping patterns on track, but advances in technology such as jet planes and brightly lit smartphones can confuse things.

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Over many thousands of years, the human body has refined its master clock – a group of neurons in the brain dubbed the suprachiasmatic nuclei (SCN) – and then modern life happened. Working night shifts, taking long-haul flights, and even staring at smartphone screens can confuse the brain’s timekeeper.

The age of technology isn’t necessarily good news when it comes to sticking to a natural sleep-wake pattern. Services often need to be kept running 24/7, and while automation helps, somebody, somewhere, still needs to be awake to keep an eye on things. There’s no shortage of modern disruptions to the circadian rhythm, which takes its name from the Latin for ‘about a day’ and matures as we grow.

Body clock studies

Fortunately, there’s a degree of resilience. And there have been some fascinating experiments to figure out the capacity of the human body clock to keep ticking. In 1962, Michel Siffre – a French underground explorer, adventurer, and scientist – spent two months living underground and discovered that his body’s circadian rhythm was preserved despite the lack of light cues.

Siffre later (in the 1970s) spent 6 months in a cave where his body adjusted to a 48-hour sleep-wake cycle – observations that have been used by NASA in understanding the effects of space travel. However, not everyone is willing to put their body through such an ordeal. And, taking things to the extreme, it would be unethical to find the point at which our body clock breaks down completely.

This is one of the reasons that researchers in Canada and the UK are using mathematical models rather than volunteers to discover how noise – in other words, disrupters such as long-haul flights or smartphone glare – impacts body clock performance.

Another motivation for using equations rather than people is that it’s relatively straightforward to scale up from simulating the dynamics of a single circadian gene to considering how a much bigger network would behave. Comparatively, in the lab, it would be extremely difficult to measure how similarly large groups of neurons respond to changing conditions.

“The results correspond to the probability of finding a neuron at a specific state in the gene expression profile,” Stéphanie Abo – lead author of the study, published recently by the Society for Industrial and Applied Mathematics and also available as a preprint on arXiv – told TechHQ.

And when the mathematical representation of the human body clock has been completely broken by too much noise, that profile becomes flat.

SCN is known as the master body clock, and the seesaw effect of rising and falling protein levels help to guide our body through the cycle of day and night. There are external cues too, such as light, food, noise, and temperature. “The liver acts as a circadian clock, to anticipate when food will come,” Abo points out.

How does the human body clock adapt to space travel?

Understanding circadian rhythms in space. Experiments have been performed by crew aboard the International Space Station (including Koichi Wakata, pictured in the photo, a Japan Aerospace Exploration Agency flight engineer) to examine how long-term spaceflight affects the human body clock. Image credit: NASA.

Modelling neurons as coupled oscillators

In the mathematical study, the group – which is associated with the Department of Applied Mathematics, Cheriton School of Computer Science, Department of Biology, and School of Pharmacy at the University of Waterloo, Canada; and the Mathematical Institute at the University of Oxford, UK – models neurons as coupled oscillators.

When the large population of oscillator neurons that comprise the circadian master clock are in sync, they produce a strong, coherent signal that drives the body clock. As the noise level increases, it becomes harder for the neurons to find their rhythm. But, as mentioned, the system is robust to a certain degree. In fact, small disruptions actually make connections between neurons stronger, based on findings from the simulations.

What was also unexpected was how multiple disruptions to the circadian rhythms over time added up and made it even harder for the body clock to recover. And there could be lessons there for anyone who regularly finds themselves out of sync.

Recapping Siffre’s experiments underground, he lacked light, but still made time to eat and drink regularly and take plenty of rest. Sleep is important – the US National Institutes of Health reminds us that sleep is as essential to survival as food and water.

And with sleep trackers becoming a popular addition to smart watches, it’s tempting to wonder whether we could have apps that help users to picture the state of their body clock. However, Abo thinks that this could be some way off, and this goes back to the difficulty of measuring what the brain is up to in sufficient detail.

However, nearer-term applications may one day include medicines or treatments that could help individuals with weak or impaired circadian rhythms. “If you decrease the rate at which the proteins are degrading, it’s possible for the system to sustain more noise without breaking down,” Abo explained.

The mathematical model is an efficient way for the researchers to test various hypotheses, and the next step for the team is to make the simulation more representative of how the body works. The current system assumes that all neurons are connected to each other, but that may not be the case in reality.

Some of the body clock’s connections could be stronger than others. For example, people are different – some of us are night owls, and others are early birds. Also, we don’t necessarily experience disruptions to our body clock to the same degree.

It’s clear there’s much more understanding to be done. However, those lessons are considerably less painful to learn when they can be performed mathematically rather than having to experiment on the body clock in real life.