Rat whiskers demonstrate active sensing

The whisking of a rat’s whisker is a classic example of “active sensing” – in other words, sensing that involves movement. Prof. Ehud Ahissar studies rat whisking in order to understand how mammals perceive through all types of active sensing; without the continuous movement of whiskers, fingertips or eyes, our perception of our surroundings would be lacking. (If you don’t believe us, try feeling the texture of your shirt or desktop without moving your fingers. You can’t stop your eyes – as you read this, your eyes are actually moving back and forth in tiny movements.)

In the latest research in his lab, postdoctoral fellow Dr. Avner Wallach and Dr. Knarik Bagdasarian managed to decode the signal that is sent from the clump of nerve endings at the base of the whisker to the rat’s brain. They accomplished this by creating a machine-brain interface, the machine recreating the whisking muscles’ movement and intercepting the nerve endings’ signals.

The amazing thing the scientists realized is that the tiny clump of nerve endings inside the follicle actually performs a complex calculation. Before the signals ever hit the brain, they are already processed. That is, instead of, say, receiving signals that the whisker is rotated 20 degrees in its socket, the rat’s brain gets signals reporting the fraction of these 20 degrees out of  the complete cycle of whisker rotation it has “planned.” It is still unclear exactly how the nerve endings perform this calculation.

That both complicates and simplifies the picture of sensing; the information fed to the brain is preprocessed and thus molded by the “mindless” sensory organ. On the other hand, the brain may perform more quickly and accurately when it works with high-quality information.

Ahissar says that the picture that is emerging from his work and that of others is of sensory organs that are much more than passive relays of signals to the brain. They play an active role in creating perception, both in reaching out and moving within their environment, and in processing the sensory information. In trying to untangle the role each part plays, he is coming to understand how interconnected they are.