MIT researchers, using a specially designed high speed camera, have been studying how rodents use their whiskers to observe the environment around them, hoping the knowledge will help with understanding how humans use tactile sensory perception.
What might a whisker-based sensation feel like? Imagine sweeping a stick across a picket fence. The frequency of vibrations depends on the spacing between the pickets, but the sensation in the hand is also affected by the length and flexibility of the stick and the speed of its movement.
Likewise, Moore [Christopher Moore, member of the McGovern Institute for Brain Research at MIT and senior author of the study -ed] reasoned, the whiskers’ movements and mechanical properties must influence the information that they relay to the brain. The whiskers are arranged in a pattern on the snout, with the shortest ones at the front. Experiments with isolated whiskers had demonstrated that, like harp strings, shorter whiskers are ‘tuned’ to resonate at higher frequencies, creating a map of frequency information within the brain. But until now, no one had managed to see the detailed pattern of whisker movements in freely behaving animals.
Like the famous images MIT’s Harold “Doc” Edgerton made of bullets going through apples, the slow-motion version of these new movies provides the first glimpse of the micromotions that the whiskers transmit to the rat brain.
“We knew from watching rats’ behavior that there must be whisker micromotions that were too rapid to measure using available recording techniques,” explains Jason Ritt, a postdoctoral scientist in Moore’s lab and first author of the study. Ritt therefore spent several years developing a video system that captures whisker movements at a rate of 3,200 frames per second — 100 times faster than typical home videos — and an automatic tracking system to analyze the resulting deluge of video data, about 1 gigabyte per second.
For the experiments, the researchers trained rats to choose either a smooth or a rough surface using their whiskers. Correct choices were rewarded with chocolate milk, and the whisker movements were captured on video. Analysis of the video revealed an unexpectedly complex pattern of movements, including periodic ‘waves’ of motion when the rat touched a smooth surface, and irregular, large and high-velocity movements when contacting a rough surface.