The rodent whisker sensory system is particularly intriguing because it is "active": the animal generates sensory signals by palpating objects through self-controlled whisker motion (just as we move our fingertips along surfaces to measure their tactile features).
In a new study, Dr. Moritz von Heimendahl and colleagues at the International School for Advanced Studies combine high-speed videography with neural recordings from somatosensory cortex to show that it is possible to use firing patterns to predict the decisions of rats as they contact textures in their environment.
Rats touched rough or smooth textures with their whiskers and turned left or right for a reward according to the texture identity.
Monitoring behavior with high-speed videography, the scientists found that on trials when the rat correctly identified the stimulus, the firing rate of cortical neurons varies during a window of a few hundred milliseconds before making a decision according to the contacted texture: high for rough and lower for smooth.
This firing-rate code is reversed on error trials (lower for rough than smooth). So when cortical neurons report the wrong stimulus, the rat, "feeling" the signals of its cortical neurons, fails to identify the stimulus.
They conclude that barrel cortex firing rate on each trial predicts the animal's judgment of texture.
This experiment begins to elucidate which features of cortical activity underlie the animal's capacity for tactile sensory discrimination.
Citation: von Heimendahl M, Itskov PM, Arabzadeh E, Diamond ME (2007) Neuronal activity in rat barrel cortex underlying texture discrimination. PLoS Biol 5(11): e305. doi:10.1371/journal.pbio.0050305
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