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. Their work is published online this week in the open-access
journal PLoS Biology.
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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