Friday, 26 April 2013

Decoding Touch: Rats Detect Textures With Their Whiskers

Apr. 23, 2013 — With their whiskers rats can detect the texture of objects in the same way as humans do using their fingertips. A study, in which some scientists of SISSA have taken part, shows that it is possible to understand what specific object has been touched by a rat by observing the activation of brain neurons. A further step towards understanding how the brain, also in humans, represents the outside world.

We know the world through the sensory representations within our brain. Such "reconstruction" is performed through the electrical activation of neural cells, the code that contains the information that is constantly processed by the brain. If we wish to understand what are the rules followed by the representation of the world inside the brain we have to comprehend how electrical activation is linked to the sensory experience. For this reason, a team of researchers including Mathew Diamond, Houman Safaai and Moritz von Heimendahl of the International School for Advanced Studies (SISSA) of Trieste have analyzed the behavior and the activation of neural networks in rats while they were carrying out tactile object recognition tests. 

During the experiments researchers observed the performance of rats -- the animals were discriminating one texture from another -- along with the activation of a group of sensory neurons. "For the first time the study has monitored the activity of multiple neurons, while until now, due to technical limitations, researchers had examined only individual neurons," explains Diamond, who heads up the Tactile Perception and Learning Lab at SISSA. "The activity of such groups of neurons is represented in our model as multi-dimensional clouds, comprising as many dimensions as the number of cells under examination (up to ten). We have observed a different cloud for the contact with each different texture." 

By analyzing the "clouds," Diamond and his colleagues were able to successfully decode the object contacted by the rodent. "Our method is so accurate that when the rat would mistake one object for another, the decoding would also indicate a different object from the one actually touched. And this happened because the representation made by the brain -- and, as a consequence, our decoding -- appeared like that of a different object. Hence the error." 

Diamond's team has no intention of stopping here. "In real life, we generally recognize objects using more senses all together, in an integrated manner. We use touch and sight at the same time, for instance," explains Diamond. "For this reason we are now working on new experiments employing more neurons, with more complicated stimuli, and more senses, to build 'multimodal' representations of objects." 


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