Twitching and twanging rat whiskers

Widely used as a model system for studying sensory processing, rat whiskers have been much studied in isolation or in anesthetized animals because the little beasts move very fast. But now a team of neuroscientists at MIT has analyzed the sensing behavior of free-ranging rats. And the researchers uncovered some important new details. If you draw one end of a stick across a wall, you can sense the wall’s texture through the stick, but the stiffness of the stick matters. Similarly, a rat sweeps its whiskers across a rough surface, where they stick, then slip, then twang at a resonant frequency when they next get stuck. Even on smooth surfaces, the whiskers’ elasticity allows for frictional stick–slip events, which are smaller and more regular than those from rough surfaces. The researchers, led by Christopher Moore, deduce that resonance is more than just an oscillation; it provides a filter for information transduced from the surface contact. Key to the work was the technology, developed by Jason Ritt, to acquire 3200 frames—about 1 gigabyte of data—per second at about 100-micron resolution and then track individual whiskers frame-by-frame through the deluge of images. The range and diversity of actual motions exceeded any seen in previous, more limited studies. The mechanical processes are transformed to neural processes through follicles at the whiskers’ base. An important next step, “which is daunting,” says Moore, is to simultaneously monitor brain activity. (J. T. Ritt et al., Neuron 57, 599, 2008.http://dx.doi.org/10.1103/PhysRevLett.57.599 )