News & Events Bear Necessities

It’s fair to say that mathematicians rarely get to work with bears. “Wow, that’s kind of cool and different,” said Associate Professor of Mathematics Tanya Leise on being asked to co-author a study on whether their circadian clocks “keep ticking” during their winter dormancy period.

The 2016 study, published in Frontiers in Zoology, took place at the Washington State University Bear Center, where grizzly bears (orphaned and unable to live in the wild) can be analyzed in captivity. Researchers also culled data from wild bears denning nearby.

The takeaway is in the study’s title: “The Bear Circadian Clock Doesn’t ‘Sleep’ During Winter Dormancy.” In other words, Leise and her fellow researchers found that these daily biological processes do not grind to a halt, as was once assumed.

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How did they determine this? By equipping the captive bears with monitors (think: big Fitbits) that measured their patterns of movement, and also by logging the bears’ body temperatures and responses to light exposure. Plus, they examined cell cultures taken from the captive bears.

This data gathered in captivity is, for humans, captivating in its implications: For the past hundred years, we have lived in an unprecedented era of light disruption of our own circadian clocks, which are tied to the light/dark cycle. The early 20th century brought us the electric grid. In the early 21st, there’s also the ever-present light of computer, tablet and smartphone screens.

And scientists speculate that this light disruption of the natural world—plus modern circadian-altering phenomena like jet lag and shift work—may be tied to rising rates of obesity, diabetes, depression and bipolar disorder. 

Indeed, circadian rhythms help regulate patterns of daily biological processes, such as hormone production and cell regeneration. Millions of little circadian clocks, on the molecular level, take their cue from a master clock in the brain—namely, the suprachiasmatic nucleus (SCN)—which tries to pinpoint when dawn and dusk are happening, and sends that information to the rest of the body.

Leise was the only mathematician on the WSU bear project; other contributors came from neuroscience, biology, zoology, ecology and other disciplines. Why add a mathematician to a scientific study? “The data is getting complex enough that it’s hard to interpret at face value,” she explains.

Leise crunched the numbers using “robust wavelet transforms,” a mathematical technique that detects frequencies in time series. In a recording of a piece of music, for example, wavelet transforms would detect the sequence of notes being played. With the bears, it was all about gauging the frequency of movement over the course of a day, and how this related to light exposure. Leise also created and analyzed mathematical models that use probability distributions and statistical inferences across a spectrum of data.

Today, Leise is firmly in the inner circle of circadian research, with 21 publications on the subject since 2006. She has studied not just bears but also mice, hamsters and fruit flies. Currently, she’s most excited by one hypothesis, backed by her data, about how circadian rhythms get synchronized in the body. The process seems to be much more complex than the SCN directing from the top down.

To explain the hypothesis, Leise says it helps to picture cells as pendulum clocks in a room: “Initially, they’re all swinging together, but over time, some stop swinging wide, others go still, some swing out of alignment. Normally, you’d connect all the clocks to a rope so they’d swing in sync (like the SCN giving out direct orders). But my analysis is that some cells also ‘kick’ other cells so they’re not so tight together. To reset the clocks, you need a little messiness.”

Grasping how these clocks work in other animals is a big step toward developing therapies to fix them in humans. Which is why, when it comes to circadian patterns, Leise keeps bearing down.