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Behavioral and electrophysiological study of spatial pattern discrimination in the rat

Abstract : The rodent whisker system is a widely used model to study behavioral and neurobiological processes underlying tactile perception, in particular during the exploration of an object shape, localization or surface roughness. The general goal of this Ph.D. work was to explore the sensori-motor strategies involved in a tactile discrimination task, as well as the neuronal activity underlying such ability. Similarly to human fingertips scanning an object, rodents are able to sweep their whiskers against surfaces in a rhythmic fashion (a process called whisking) to analyze spatial details. In most laboratory tasks, rats discriminate spatial patterns by whisking on them successively. Based on the life of these animals in the wild, we hypothesized that rodents could discriminate spatial patterns without whisking. To demonstrate this, we developed a novel task inciting the rats to touch the stimuli by running past them at such high speed that the time needed to complete a whisking cycle is not available. Rats learned to discriminate a surface with a series of vertical bars regularly spaced from a smooth surface. Both whiskers and neural activity in the primary somatosensory cortex were involved during the discrimination process. Rats could also discriminate an irregular series from the regular one. We showed that rats do not whisk on the stimuli, and that they orient their whisker arrays towards the rewarded stimulus as soon as 60ms after the first possible contact (Kerekes et al., 2017). These results demonstrate that rats can discriminate stimuli without actively whisking. A second project of this Ph.D. work focused on the analysis of whisker deflections and thalamo-cortical neuronal responses evoked in the anesthetized rat by the stimuli passing on the whiskers mimicking the tactile condition during the task. Preliminary results show the presence of high-acceleration events occurring during whisker stimulation. These events evoked significant cortical responses, that differed according to the stimulus type (irregular or regular series). Four rats have been recorded for this study, two of them were trained on the discrimination task, and the two others were trained on a non-tactile task on the same maze. With this data, we plan to search for potential effects of learning on neuronal treatment of tactile inputs. Both the development of the novel discrimination task and of neuronal recordings in anesthetized and awake rats will allow to tackle new questions on tactile discrimination processes, such as how spatial regularity or irregularity are encoded and how this encoding can be modulated by learning.
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Pauline Kerekes. Behavioral and electrophysiological study of spatial pattern discrimination in the rat. Neurons and Cognition [q-bio.NC]. Université Pierre et Marie Curie - Paris VI, 2017. English. ⟨NNT : 2017PA066551⟩. ⟨tel-01897480⟩

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