טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGarion Liora
SubjectTexture-Dependent Neuronal Assemblies in Layer 2-3 of the
Rat Barrel Cortex in-vivo
DepartmentDepartment of Medicine
Supervisor Professor Jackie Schiller
Full Thesis textFull thesis text - English Version


Abstract

One of the fundamental roles of the somatosensory system in general and the rat whisker system in particular is to identify and discriminate between different textures.

In this study we concentrated on understanding how texture coarseness is represented in the barrel cortex of the rat. To mimic the way rats move their whiskers actively during exploration, we used artificial whisking paradigm on different textures. The neuronal activity during the artificial whisking was recorded using two-photon calcium imaging from several dozens of bulk loaded neurons simultaneously. Our findings suggest a new texture coding mechanism in layer II/III of the rat barrel cortex, based on single neuron selectivity to different texture coarseness. Texture selective neurons were almost exclusively confined to the barrel boundaries, whereas septal neurons were non-responsive or non-selective to texture coarseness.

In addition, we investigated the spatial mapping of texture coarseness onto cortical layer II/III. Spatial mapping of various sensory features is a fundamental organizational principle in the CNS, which has been observed in many functional modalities and multiple cortical areas. Since rodents relay mostly on their somatosensory and olfactory senses we believe that somatosensory maps are more likely to emerge in the rat’s cortex.

Our high resolution two-photon mapping revealed a new spatial organization of texture coarseness representation in layer II/III of rat barrel cortex. We found that neurons with the same preferred texture coarseness were spatially clustered and organized in stripe-like regions, with a tendency for representation of coarser textures in the barrel perimeters while the smoother textures tended to be represented more centrally.

In the second part of this work we examined the response kinetics of layer II/III neurons to repetitive artificial whisking against textures. We observed different degree of adaptation in layer II/III neurons ranging from rapidly to slowly adapting calcium responses. When roughly dividing the neurons to two subpopulations we observed a spatial clustering according to the adaptation preference, with neurons tended to be spatially clustered in patches of either rapidly or slowly adapting neurons across cortical layer II/III.

These findings indicate that layer II/III neurons perform high hierarchical processing of tactile information, which is coded in sub-groups of neurons spatially mapped onto layer II/III of the barrel cortex. It is yet unknown what is that functional advantage of using spatial sub neuronal mapping, one such advantage may serve for efficient connectivity of the cortical network.