Nestled in dark burrows, with a limited sense of vision, mice brush their whiskers against their environment to navigate and to detect objects around them. This behavior, termed whisking, has been extensively studied in the past few decades and has traditionally been viewed as purely an act of touch. Now Weizmann Institute of Science researchers present an entirely new, multisensory view of this process. These resounding findings, published recently in Current Biology, reveal that whisking generates subtle sounds that are encoded in the auditory cortex of mice, enhancing their perception of their surroundings.

“Whiskers are so delicate that no one had thought of checking whether they produce sounds that mice are able to hear,” says team leader Prof. Ilan Lampl of Weizmann’s Brain Sciences Department.

The study offers a unique glimpse into the complexity of natural perception, which commonly involves input from multiple senses, in this case touch and hearing. In fact humans too combine these two types of cues more often than one might think. Imagine, for example, your fingers delving into a crowded bag to search for a candy bar and the sudden, welcome rustle of the wrapper.

In the new study, Lampl’s team – led by Dr. Ben Efron, then a PhD student, who worked with Drs. Athanasios Ntelezos and Yonatan Katz – started out by recording the sounds made by whiskers probing different surfaces, including dried Bougainvillea leaves and aluminum foil. The researchers used sensitive microphones that can record ultrasonic frequencies, which are beyond the upper limit of the audible range for humans. They placed the microphones some 2 centimeters from the source of the sound, about the same distance as from the mouse’s ear to its whiskers.

Next, the scientists made entirely different recordings: They measured neural activity in the auditory cortex of mice that were brushing their whiskers against different objects. The recordings showed that the auditory networks of the mice responded to the whisker-generated sounds, no matter how subtle. When the researchers interrupted the pathways that convey the sensation of touch from the whiskers to the brain, the auditory cortex still responded to these sounds, showing that mice could process them as a separate sensory input, independent of the sense of touch.

Yet the fact that the mouse auditory system responds to certain noises does not necessarily mean that mice use them for sensing and can recognize objects by means of these noises. To explore this issue, the researchers resorted to AI. They first trained a machine-learning model to identify objects based on neural activity recorded from the auditory cortex of mice. The AI successfully identified the correct objects from neuronal activity alone, suggesting that the mice might be able to similarly interpret these cues. Next, the researchers trained another machine-learning model to identify objects on the basis of recorded sounds made by whiskers probing these objects. The two models – the one trained on neural activity alone and the one trained on sound recordings – were equally successful, which suggests that the neural responses to the whisking were caused directly by the sounds rather than by other sensory information, such as that coming from smell or touch.