14 DAY TRIAL // You see, the whiskers of a cat or rat are not adornments, but highly sensitive organs. It appears that much more sensitive than we could think: like a tuned harp, the whiskers of a rat detect various frequencies depending on their structure.
In the dark underground sewers and galleries, rats cannot use the sight. Previous studies had shown that the shorter whiskers located at the front of rats' snouts are specialized to detect vibrations at higher frequencies and the longer ones at lower frequencies. A large area of their brain cortex processes signals coming from the whiskers, so that rats really orientate using their whiskers.
"They can sense the tiniest speck on a wall with their whiskers," said Christopher Moore of the McGovern Institute for Brain Research at MIT.
But while other researches investigated plucked whiskers or anesthetized rats, the new one, published in the journal Neuron, caught the live action of the whiskers on high-speed video, helped by computer analysis, for the first time discovering micromotions effectuated by each whisker while picking up signals.
"We knew from watching rats' behavior that there must be whisker micromotions that were too rapid to measure using available recording techniques," said lead researcher Jason Ritt, a postdoctoral researcher at MIT.
Ritt used a video system taking 3,200 frames per second (100 times more rapidly than typical home videos) and a computer tracking system processing this huge video data (around 1 gigabyte per second).
Trained rats had to detect, using their whiskers, either a smooth or a rough surface for receiving a chocolate milk prize. "Each one of the whiskers is touching the surface and picking up a different frequency band," said Ritt.
The high-speed video tracked down tiny vibrations of individual whiskers, while computer analyses of the recordings showed how the different surfaces were associated with different micromotions.
"The vibrations due to the tip hitting the surface reach the base and in the rat's face the base is where all the nerve endings are. What it is going to be sensing is all the vibrations coming down the shaft of the whisker," Ritt told LiveScience.
The rough surfaces were associated with "stick-slip-ring" micromotions: a whisker hampered by a bump on a surface quickly slip forward, while its shaft shook back and forth. Smooth surfaces were connected to minute "stick-slip" oscillations.
"These patterns are larger and more complex than anything previously observed in anesthetized animals or plucked whiskers, but they are the key to a rat's perceptions and behavior," said Moore.