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Oh no! You dropped your keys on the ground, and it is too dark to see them. You might have to feel the ground with your hands, but a mouse could use its whiskers to find the keys.

Mouse whiskers, also known as the vibrissa system, are long facial hairs which are sensitive to touch and allow mice to feel around their environment. As a whisker touches something, the sensory neurons at the hair follicle activate. These neurons send electrical signals to the animal’s central nervous system, which interprets them into information about the features of the environment.

But a recent study by neuroscience PhD candidate Ben Efron and his colleagues suggested that mice may use their whiskers to explore their surroundings in ways other than the sense of touch.

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The sensory system of mice is especially useful for nocturnal animals like mice that navigate in lightless burrows and in the dark corners of our houses. Mice can use specialised muscles to move their whiskers in patterns. They can also do this by turning their head. This behaviour is called whisking. Rodents use various whisking patterns depending on whether it is running, turning or examining an object. The faster the mouse runs, the faster the whisker movements are.

The researchers behind the new study noticed that mouse whiskers make subtle sounds when they touch surfaces. They measured the electrical activity of neurons in the auditory cortex (a brain area that processes sound) of whisking mice and discovered that these sounds induce brain activity.

This happened even when the nerve connection that conveys touch sensation from the whiskers to the brain was cut, suggesting that mice can detect these sounds as a separate sensory input with their auditory system. The researchers also trained mice to recognise specific surfaces solely based on the sounds that their whiskers produced.

Scientists generally have believed that whiskers only help mice explore their surrounding via touch. But these results indicate whiskers provide sound information to mice too. Whether other animals with whiskers can do this too remains to be studied.

Integrating information from several senses in this way may help animals make a more accurate interpretation of the world around them. Like mice with their whiskers, you can acquire multisensory information about the location of your lost keys with your hands. You might not identify them based on how they feel when you tap them but the familiar sound of the keys jingling would tell you that you have found them.

Every animal perceives the world differently through the unique combination of the senses that they have. There is a secret world of sounds and vibrations around us that we cannot experience.

The way mice in the recent study identified objects based on sounds resembles, in part, echolocation that some bats and aquatic mammals like dolphins use for navigation. Echolocating bats produce ultrasounds – meaning that they are too high in frequency for humans to hear them – which reflect from surrounding surfaces. Bats can navigate their way in total darkness and detect prey such as moths by listening to these echoes.

Moths in turn have evolved acoustic defenses against echolocating bats which include the ability to detect ultrasounds, acoustic camouflage (wing scales that reduce ultrasonic echoes), decoy structures (elongated wingtips that misguide the bats to attack away from the body of the moth) and emitting ultrasounds that compromise bat echolocation.

Lunar moth tails make an acoustic signal that seems to make bats zero in on the tail rather than more vital body parts.
Jay Ondreicka/Shutterstock

Elephants make vocalisations known as rumbles that are infrasonic, meaning that they are too low in frequency for humans to hear them. Elephants, however, seem to use rumbles for long distance communication. Rumbles travel through air as sound signals and through the ground as seismic signals which can travel up to 6km.

It’s not completely clear how elephants detect seismic signals. Detection may happen through vibration-sensitive organs in their feet and/or through bone conduction hearing. During bone conduction hearing, vibrations do not enter the inner ear as airborne sounds but as vibrations of bones and tissues. You can experience this by placing a vibrating tuning fork on the bony part of your head behind your ear or on your tooth. Suddenly, you can hear the tuning fork vibrating loudly.

Why should we be interested in this secret world that cannot be detected by human senses? First, human-generated environmental change, which includes noise pollution, poses significant threats to many species and ecosystems.

For example, maritime noise interferes with sound communication of whales and dolphins while human-made noise on land disturbs nesting birds. To protect animals from these harmful effects, we need to understand how their sensory systems are affected.

Secondly, bio-inspired innovations are waiting to be discovered. So keep in mind next time when parking a car with ultrasound-based parking sensors that echolocating bats have had access to this navigation technique for more than tens of millions of years.

Tommi Anttonen does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.