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Complexities of insect ears

Humans do not have a monopoly on eardrums, they are common among insects. Interestingly, crickets show more elaborate control over tympanal membranes than humans.
Complexities of insect ears
Researchers, with EU support of the project 'The tympanal ears of insects: Structural solutions to acoustic signal analysis' (INSECT EARS), made an exciting discovery that could have important implications for the development of novel devices. It could also shed light on potential mechanisms of disruptions in insect communication networks, many of which have severe ecological consequences.

The tympanal organ consists of a thin tympanal membrane backed by an air-filled cavity and supplied by sensory nerves. Scientists compared the tympanal hearing organs of three different types of crickets (tree crickets, locusts and field crickets).

Researchers used sophisticated experimental techniques together with biophysical models of the membrane systems to elucidate the vibrational mechanics of insect tympana. They focused on previously unknown differences in membrane architecture related to differences in acoustic functions as a pathway to rational design of miniature acoustic sensors.

Energy localisation in tree crickets and locusts is accomplished by asymmetric corrugations in the membrane architecture. This makes the membrane stiffer in one direction than another, concentrating vibration at the point of neuronal attachment. A very steep thickness gradient in a concentric pattern and a membrane-liquid interface embedded in the membrane of locusts at its centre enable frequency sensitivity.

INSECT EARS scientists also discovered a type of active mechanics in tree crickets that is similar to cochlear amplification seen in humans and by which they enhance mechanical oscillations of the membrane to amplify incoming sounds. Unlike humans, this mechanism can be turned on and off, it suppresses low-frequency noise and it can modify its response to cope with temperature changes.

INSECT EARS provided valuable new insight into the biophysical mechanisms of insect hearing, which should have major impact on signal processing in artificial microsensors. Outcomes are expected to influence fields as diverse as neurobiology, ecology and environmental protection.

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