Scientists from Washington University in St. Louis have discovered a purpose for many of our brain cells that were previously believed to be "inactive," or mere "gap fillers."

The finding involves humdrum cells known as astrocytes, a type of glial cell which didn't seem to have much going on other than having charismatic starry shapes. Glial cells, or glia, are non-neuronal cells that make up as much as 90 percent of cells in the brain. In fact, glia are one of the main sources for the unfounded myth that people only use 10 percent of their brain, since these cells are not typically known for the higher-order tasks that produce our mentality or behavior.

But that understanding could soon change. After figuring out a way to independently control astrocytes in the brains of rodents, Washington University researchers discovered that they could also control the animals' sense of time, according to a press release.

“We had no idea they would be that influential,” said Matt Tso, the first author on the paper.

The astrocytes in question were located in an area of the brain known as the suprachiasmatic nuclei (SCN), which is found in the hypothalamus and is primarily known for regulating our internal clock, or natural sense of time. There are about 20,000 active, firing neurons in the SCN, but there are around 6,000 astrocytes there too, and scientists have never fully understood why.

Surprisingly, when the researchers turned off a gene in the astrocytes known as a "clock gene," which helps normal cells keep rhythm, it wasn't just the astrocytes that seemed affected. The rodents themselves seemed to lose their normal sense of rhythm too, as if the astrocytes were playing a key role in regulating the animals' circadian clock.

We know that mice have circadian clocks that last for about 23.7 hours, because even mice in constant darkness will start running on a wheel every 23.7 hours. (Humans also have internal clocks, but ours run a tad overlong, on a daily cycle of 24 hours, 11 minutes.) Mice that had their astrocytes tinkered with, however, were way off. They began running on their wheels anywhere from 1 to 2 hours late, and seemed out of rhythm in general.

"[These results] suggests that the astrocytes are somehow talking to the neurons to dictate rhythms in the brain, and in behavior," team member Erik Herzog told The Scientist.

While the full extent of how and why astrocytes control our circadian behavior is still poorly understood, this research demonstrates that there's a lot more going on than previously believed. The research also begs the question of what role glial cells are playing in our mentality throughout the rest of the brain.

Not only does the study officially bust the myth that we only use 10 percent of our brain cells, it also proves that there are essential neurological processes going on in our heads that we've only just begun to understand.