'Singing' Rats Used to Study Vocal Changes in Aging Humans

A study of the high-pitched "singing" done by rats may help scientists unravel new clues about vocal degradation in humans as we age.

In the study, older rats were able to reduce vocal problems related to their age by undergoing vocal training. The vocal problems faced by aging rats are similar to many related vocal problems faced by aging humans, including the loss of vocal intensity that accompanies changes in the muscles of the larynx as we age.

Aaron Johnson, a speech and hearing science professor at the University of Illinois, led the research along with colleagues from the University of Wisconsin.

Johnson said he became interested in vocal research on aging populations after working with the elderly as a former classical singer and voice coach.

"We know exercise strengthens the limb musculature, but we wanted to know if vocal exercise can strengthen the muscles of the voice," Johnson said. 

Johnson turned to rat models to see if vocal training could have an effect on the strength and physiology of the vocal muscles in humans. Because rats and humans utilize similar mechanisms to vocalize, Johnson said the rats make an ideal test subject, even though we cannot hear them ourselves.

Although rats' ultrasonic vocalizations are outside the range of human hearing, the sound can be recorded and played back using special equipment that allows humans to perceive them and sounds similar to chirping birds.

For the experiment, Johnson and colleagues conditioned male rats to make louder chirping noises for a food reward, effectively training their vocal muscles to produce a higher-than-average vocal intensity.

According to a report from University of Illinois, the researchers found the trained old and young rats had similar average vocal intensities, but the untrained older rats had lower average intensities than both the trained rats and the young rats that had not been trained. They also found several age-related differences within the groups' neuromuscular mechanisms. 

"Other research has found that in the elderly, there is a dispersion, or breaking apart, of the neuromuscular junction at the side that is on the muscle itself," Johnson said in the report. "We found that in the older rats that received training, it wasn't as dispersed." 

Johnson said the "singing rats" were the "first evidence that vocal use and vocal training can change the neuromuscular system of the larynx."

"While this isn't a human study, I think this tells us that we can train ourselves to use our voices and not only reduce the effects of age on the muscles of our voices, but actually improve voices that have degraded," Johnson said.