Nosy computation. Scanning the head of a rat in a laser scanner and plotting its whiskers on a graph (bottom) allowed the researchers to reconstruct a 3D model of its head (top left).

(top left, right) Mitra Hartmann; (bottom left, right) R. B. Towal et al., PLoS, 7 (April 2011)

Virtual Whiskers Probe Sense of Touch

Rats can rummage through a trash heap or scamper through an underground tunnel with their eyes closed. That’s because their whiskers have evolved to give them a detailed sense of their surroundings, even more precise than in animals such as cats and dogs. A new computer model of how our twitchy-nosed friends move their whiskers could lead to a better understanding of how the brain processes the sense of touch and even speed the development of whisker-covered robots.

The lack of whiskers is a uniquely human trait among mammals, one that forces us to rely on sensory input from our fingers for most of our tactile information. The problem with studying how these sensations inform the brain in humans, however, is that the hand is extremely complicated. “It has a ton of muscles and skin elasticity, and we don’t know where the sensors are,” says biological and mechanical engineer Mitra Hartmann of Northwestern University in Evanston, Illinois.

Wiggling whiskers. The 3D model realistically represents how a real rat investigates its surroundings.
Credit: Mitra Hartmann, Northwestern University

Whiskers, she says, are much simpler. Each one of a rat’s 60 whiskers ends in a follicle below the skin. As the whisker touches an object, the follicle recognizes how much pressure is being applied and how much the whisker has bent. It can then relay this information to the brain, which correlates input from all 60 whiskers to create an idea of the shape of the object the rat is exploring.

To recreate this sensation yourself, Hartmann suggests that you close your eyes and pick up a coffee cup from your desk. Consciously or not, your fingers touch the cup one after another in a certain order and at different distances from one another, ascertaining the cup’s size and shape. All the while, your brain is combining this information and turning it into a three-dimensional (3D) perception.

A rat moves, or “whisks,” its whiskers in the same way. Each whisker moves independently of the others and of the muscles in the cheek, and each feeds into an individual cluster of neurons in the brain. “It’s a beautiful thing,” says computational biologist Tony Prescott of the University of Sheffield in the United Kingdom, who was not involved in the project.

Hundreds of researchers study whisking, and to help them out, Hartmann and her colleagues decided to construct a 3D computer model of the rats’ whiskers, which they describe online today in PLoS Computational Biology. The team placed rats in a 3D laser scanner and scanned their noses to map out the exact morphology of their whiskers and cheeks. By applying previous knowledge of how a rat whisks in different situations, they created a computational model that realistically simulates real rats’ whiskery explorations (see video).

“This is very important work for a number of reasons,” Prescott says. In the short term, the whisker model, which is open source, may help neuroscientists better understand tactile sensory input. Hartmann doesn’t expect it to replace rats in the lab, but it might help predict how informative neuroscience experiments using whiskers will be.

The model may also help speed the development of rat-inspired biomimetic robots, which Hartmann and Prescott are currently building. In pitch-blackness, a bewhiskered robot could use tactile sensations in place of cameras to glean a picture of its surroundings. Additionally, Hartmann suggests that the ability to feel fine resolution could help a robot perform tasks such as finding a crack in a pipe. Although she says that such sophisticated whiskers are still a long way off, “it’s extremely exciting” to think about their possible applications.