Bushcrickets’ Ultrasonic Hearing Organ May Hold the Key to Advanced Hearing Aid Technology
Bushcricket hearing organs, similar to those of humans, could inspire the next generation of acoustic sensors, hearing aids, and biomedical imaging techniques
--by Heather Kathryn Ross
Colombian bushcrickets, also known as katydids, have some of the oddest ears around. They carry four separate eardrums on their forelegs, but until now, scientists had no idea how sounds detected by the eardrums traveled to the insect’s sensory receptor cells for processing.
Dr. Fernando Montealegre-Z grew up in Columbia and was fascinated by these tiny creatures from an early age. Now at the University of Lincoln’s School of Life Sciences, he’s finally solved the mystery of bushcrickets’ highly adept hearing. His team discovered a fluid-filled vesicle, or sac, that mediates the process of converting sound waves collected by the eardrums into mechanical and electrochemical energy.
Bushcrickets can hear ultrasonic sounds in the range of 130-150 kHz, and can do so over extremely long distances. Compare that to a human’s puny hearing range of 15-20kHz.
“Sounds at these [extremely high] frequencies suffer excess attenuation and would not transmit far in a rainforest environment, therefore limiting long-range communication," said Montealegre-Z in a press release. "Yet [bushcrickets] manage to listen to one another from far greater distances. We don't know how they do it, but we do think this sensitivity comes, in part, from the ‘Auditory Vesicle.’”
The Expert Take
Bushcricket ears, strange as they look, are not so different from our own. Montealegre-Z’s newly identified vesicle acts in much the same way as a human middle ear, in that it transfers airborne vibrations to the inner ear, where they are converted into neural impulses. The implications of his discovery for the development of selective, sensitive hearing aids and other medical devices are potentially enormous.
"The ears of this bushcricket are teaching us that complex hearing mechanisms can take place in very small ears,” said Daniel Robert, a professor at the University of Bristol's School of Biological Sciences and a member of the research team. “As such, we are learning how evolution has come up with very small, efficient, and sophisticated microphones. We now have to learn how to make one like this."
Though it will undoubtedly be a while before bushcricket-based audio devices reach the market, the potential applications of these “engineered bio-inspired systems” seem limitless.
"Dr. Montealegre's findings will make a valuable contribution to our search for the next generation of ultrasonic engineering technologies,” said Dr. James Windmill of the Centre for Ultrasonic Engineering at the University of Strathclyde. “By improving our understanding of insect hearing and sensory systems, we can incorporate new ideas and techniques into a wide range of technologies, including hearing aids, biomedical imaging systems for hospitals, and ultrasonic non-destructive evaluation to assess the structural integrity of buildings and bridges.”
Source and Method
This research focused on the bushcricket Copiphora gorgonensis from the National Park Gorgona in Colombia. Scientists used integration laser Doppler vibrometry and micro-CT (computed tomography) scanning to identify the “Auditory Vesicle” and to determine how it works in conjunction with the animal’s other hearing organs.
Montealegre-Z and his colleagues are planning field research to study katydids in their natural environment in Colombia. Funded by a National Geographic grant, the new research entails attaching special electrodes to the katydid sensory system, which will allow scientists to hear the same sounds the insects do.
A study conducted by University of Iowa researchers in 1999 and published in Current Opinion in Neurobiology concluded that though insects use a wide array of external organs to transform sound waves into mechanical signals, their microsensory transducers, called chordotonal organs, are very similar.
These chordotonal organs also resemble the hairs in the inner ears of humans and animals that help translate sound waves moving through the fluid of the inner ear into neurochemical signals. That these structures are similar in insects and mammals suggests that they may have evolved from a common organ or cell complex.