SAN DIEGO--The rat is not normally considered a whistler extraordinaire, but perhaps that's because its technique is concealed deep in its throat instead of around its mouth. The animals purse their vocal cords to produce sounds inaudible to many animals, researchers reported here last week at the Society for Neuroscience meeting.
There's a lot of chatter outside the range of human hearing. Bats, for example, bounce ultrasonic sound waves off insects to pinpoint their prey's location, direction of motion, and speed. Ultrasonic vocalization among rats serves different purposes, such as alerting fellow rats without tipping off predators. Precisely how rats produce these noises has remained a puzzle.
To solve it, otolaryngologist Ira Sanders and his colleagues at the Mount Sinai School of Medicine in New York City anesthetized a group of rats and inserted small digital cameras down their throats to videotape the vocal folds. By stimulating an area of the brain stem with electricity, they could trigger the ultrasonic vocalizations. Sanders' team watched as the folds, instead of vibrating as they do to produce audible sounds, formed a small hole about a millimeter or two in diameter, through which the animals forced air. "They're essentially whistling through that," says Sanders.
"It's a very good study," says neuroscientist June-Seek Choi of Yale University, who notes it clears up the mystery of ultrasonic vocalization in rats. Still, Sanders is baffled by the rats' ability to rapidly alter the frequency of their ultrasonic chirps without no obvious change in the appearance of their vocal folds, and he plans to explore this next.
Sanders's home page
Echolocation in bats
Echolocation in dolphins