Columnar modules can be regarded as the basic unit of cortical information processing. We are interested in the processing of tactile information in the primary somatosensory cortex where, in rodents, barrel-associated columns can be clearly identified. Cortical columns, however, display a large cellular heterogeneity. Thus, we chose the analysis of functional and structural connectivity of single, defined neurons, in vitro and in vivo in order to determine the basic principles of columnar information processing.
Left panel diagrammatically shows the whisker-to-barrel pathway in rodents. The whiskers (vibrissae) sense the properties of discrete parts of the outside world with their associated mechanoreceptors, sitting within the follicles. This tactile information is transmitted via trigeminal afferents to the modules located in the brainstem nuclei (barrelettes), form there to the thalamus (barreloids) and finally to the primary somatosensory cortex (barrels), which leads to conscious perception of tactile stimuli. Right panel shows that a preferential connection exists between those modules coding for the information coming from the same whisker in the map. In the cortex, an integration of information, sensed by a specific set of whiskers, within microcircuits of the different layers (I-VI) of the barrel-related column takes place. Thus, a unified percept can be formed from the originally discrete parts of information of certain object (i.e. walnut).
In a new approach, we search for mouse mutants or knock outs which display obvious distortions of the cortical Bauplan. We will examine all modules of the whisker-to-barrel pathway, i.e. barrelettes in the brainstem, barreloids in the thalamus and barrels with their associated functional columns in the neocortex, in order to exclude that a certain cortical phenotype is but a copy of subcortical patterning defects. We have started to investigate mouse models such as barrelless (or: GAP-43 knock outs) for their disturbed "verticality" as well as reeler (or: VLDLR/ApoER2-, Dab1 knock outs) for their disturbed "horizontality". The goal is on the one hand to determine, up to which degree of cortical disorganization a developmental plasticity of the cortex can still secure the formation of columns. If such animals without cortical columns will be identified, then, on the other hand, "structural defect-loss of function studies" will be conducted.
These goals we want to reach with a multimodal, highly interdisciplinary approach.