Infoscience

Thesis

The excitatory neuronal microcircuit of the C2 column in the mouse primary somatosensory cortex

Rodents are nocturnal animals gathering information about their surroundings by using highly sensitive detectors laid out on their snout. Like humans use their fingertips to apprehend textures, rodents use their whiskers to build a spatial representation of their environment, locate objects and discriminate fine textures. The most remarkable feature of the somatosensory whisker system consists in the isomorphic correspondence of each whisker with discrete cytoarchitectonic units in layer 4 of the primary somatosensory "barrel" cortex. These layer 4 barrels are the first step towards the integration of the sensory information within the neocortex and form the core of each cortical barrel column. To further our understanding of sensory processing, it becomes evident that studying the synaptic wiring of a specific barrel column will provide useful information. In this thesis work, we specifically investigate the excitatory wiring diagram of the C2 barrel related column. The functional location of our preferred column was mapped in vivo using intrinsic optical imaging upon C2 whisker deflection. The excitatory microcircuit of the C2 barrel column was investigated in vitro using simultaneous multiple whole-cell patch clamp recordings in the current clamp mode. We show that layer 4, through its highly recurrent and strong network, acts as the main excitatory driving force, spreading information across the entire cortical column. We demonstrate that supragranular layers are involved both in intralaminar recurrent circuits and top-down relations with postsynaptic partners in specific subjacent layers. The last relay of the excitation flow consists of the infragranular layers that integrate input from the whole column, and form the output of the cortical computation. Finally, by assessing the diversity of short-term dynamics of a subset of excitatory connections, we point out the complexity of sensory processing and the long journey remaining to unravel the synaptic mechanisms underlying sensory perception.

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