An elephant’s trunk is a marvelous thing, flexible enough to bend and stretch as it forages for food, but also stiff enough to grasp and maneuver even delicate objects like peanuts or a tortilla chip. That’s because the trunk is highly sensitive when it comes to sensing touch. Scientists have determined that the whiskers lining the trunk are crucial for that sensitivity thanks to their unique structure, amounting to a kind of innate “material intelligence, according to a new paper published in the journal Science.
As previously reported, there is a long history of studying whiskers (vibrissae) in mammals. Rats, cats, tree squirrels, manatees, harbor seals, sea otters, pole cats, shrews, tammar wallabies, sea lions, and naked mole-rats all share strikingly similar basic whisker anatomies, according to various prior studies. Among other potential applications, such research could one day enable scientists to build artificial whiskers as tactile sensors in robotics, as well as learn more about human touch.
Whiskers are much more complex than one might think, both in structure and function. Rats, for instance, have about 30 large whiskers and dozens of smaller ones, part of a complex “scanning sensorimotor system” that enables the rat to perform such diverse tasks as texture analysis, active touch for path finding, pattern recognition, and object location, just by scanning the terrain with its whiskers.
Technically, the whiskers are just hairs, a collection of dead keratin cells. It’s what they’re attached to that makes them as sensitive as human fingertips. Each rat whisker is inserted into a follicle that connects it to a “barrel” made up of as many as 4,000 densely packed neurons. Together, they form a grid or array that serves as a topographic “map,” telling the rat’s brain exactly what objects are present and what movements are taking place in their immediate environment. All those barrels in turn are wired together into a kind of neural network, so the rat gets multidimensional cues about its environment. Rat whiskers also resonate certain frequencies; there are shorter whiskers near the nose, with longer ones further back, enabling rats to create a kind of “frequency map” by poking their noses all over the place