Sound waves seem to have this uncanny ability to take control of our emotions. Whether you have a special song to pump you up on game-day (E-A-G-L-E-S!) or a carefully curated playlist to help you wind down on the weekend, it’s hard to deny the effectiveness that music or specific sounds can have in altering your mood – for better or worse.
Sound’s mood-altering capabilities are not a purely human phenomenon. To further complicate the matter, sounds that we find appealing (or cannot hear) can be catastrophic or a “turn-off” for other animals. This has a lot to do with how individual species process sound and the make-up of their inner ears. Mice have much smaller ear canals which results in a drastically higher resonant frequency than humans; approximately 3.4 kHz for humans vs. 21.2 kHz for mice. For any animal, sounds that are at or near the resonant frequency of their ear canals are amplified.
Sounds that are above 20 kHz, or beyond human hearing, are referred to as ultra-sonic. In most of our work, we are focused primarily on the range of human hearing, 20 Hz – 20 kHz, but when dealing with non-human subjects, ultra-sonic frequencies must also be considered. For example, mice hear up to 90 kHz!
Metropolitan Acoustics recently investigated sound and vibration levels at a lab to determine if these factors may be contributing to the lack of breeding in two strains of mice. Initially, it was thought that the main issue was vibration caused by a local trolley line. Utilizing our proprietary sound and vibration monitoring system, we compared the data to the sensitivity thresholds for mice. While certain vibrations can stress-out mice by triggering warnings of a predator, our analysis also determined that there was something else going on that could be contributing to the lack of breeding.
Mice utilize ultra-sonic communication for territorial signals, warning signals, and even mating signals. If outside sources are generating sounds within this ultra-sonic range, it can cause stress, anxiety, and confusion, and ultimately effect their behavior, mood, and breeding habits.
We monitored sound levels up to 90 kHz in the labs to see if there were ultra-sonic sources affecting the mice. There are many devices ranging from label readers and light sensors to laptop computers that generate ultra-sonic sound levels that are 10 dB or greater than the ambient condition. In the same way that an intrusive sound can wake us up from a sound sleep or simply ruin our mood, the same goes for mice and other animals. We found that many of the mice labs had intrusive levels of ultra-sonic sound. Further investigation will help us pinpoint the sources of this noise and provide recommendations to limit their negative effect on the mice.
This time of year they say “love is in the air”, which is true in a more literal sense; love, or the potential lack-thereof, is in the airwaves! Happy Valentines Day! We hope that you all are able to spend time with your loved ones. If you get any pushback on your carefully curated playlist, just remind your loved one that science backs your mood-setting choice of tunes!