"Our sense of touch is very mysterious. You can reach into your pocket or your purse and without even looking, you can identify your keys, a coin, or a paperclip," Mirta Hartmann, who studies sensory and neural systems engineering at Northwestern University
Her lab is using rat whiskers to understand how the brain goes from the mechanics of touch to a perception. "In the same way that we use our hands to go out and actively explore different objects, rats use their whiskers," Hartmann said.
Whiskers are less complicated to study than the human hand, which has sensors all over. The response of the sensors depend on the viscoelasticity of the skin.
Rat whiskers, by contrast, have senors only at the base. In addition, "rats cannot grasp with their whiskers, they can only explore. Our hand movements are complicated because we can grasp and manipulate objects, as well as tactually explore," Hartmann noted.
She can colleagues studied the structure of the rat head and whisker array — 30 on each side of the face arranged in a regular pattern — to create their virtual model.
Rats use these whiskers to whisk objects 5 to 25 times per second. This is different than cats or dogs, which also have whiskers but aren't able to "move them back and forth that much," Hartmann noted.
The model allows the researchers to simulate the rat whisking against different objects and predict the full pattern of inputs into the whisker system as a rat encounters an object. These simulations can then be compared against real rat behavior.
"It allows us to start to simulate what's going to happen as the rat comes up to an object and explores it with its whiskers," she said.
This information, in turn, should lead to insights to what's going on in the human brain as the hand fishes around a pocket or purse.
"There's just electricity in your brain and there's just mechanical signals on your hand. And somehow your brain is able to turn that contact pattern into electricity that generates a perception," Hartmann said. "That whole process is very mysterious. We need basic research to try and figure out how that happens."
In addition, the research is being used to create robots with whiskers, which can use the motion of the whiskers to generate three-dimensional spatial representations of the environment. The technology could be used, for example, on robots designed to explore dark places.
A paper describing the research was published Thursday online in Public Library of Science Computational Biology.