They found that the volume of the midbrain - a small region of the brain that relays information for the visual, auditory, and motor systems - in the bred-for-athleticism mice was nearly 13 percent larger than the midbrain volume in the control or "regular" mice.
"To our knowledge, this is the first example in which selection for a particular mammalian behaviour - high voluntary wheel running in house mice in our set of experiments - has been shown to result in a change in size of a specific brain region," Garland, professor of biology and the principal investigator of the research project, was quoted as saying by The Journal of Experimental Biology.
In Garland's lab, selection for high voluntary wheel running in lab house mice has been ongoing for nearly 20 years, or more than 65 generations of house mice, according to a university statement.
To analyse brain mass and volume on independent samples of house mice, researchers dissected the brains into two different regions, the cerebellum, a region of the brain crucial for controlling movement, and the non-cerebellar areas.
They then weighed these sections separately.
The cerebellum is important for coordination. The midbrain is essential for reward learning, motivation and reinforcing behaviour.
Previously, species of mammals and birds with larger brains have been shown to have higher survivability in novel environments.
Researchers found that compared to regular mice, those mice that had been selectively bred for high voluntary wheel-running had significantly greater midbrain volume as well as larger non-cerebellar brain mass.