Simulations of Neocortical Columnar Oscillations

Colenso, Richard Jon Arthur (2004). Simulations of Neocortical Columnar Oscillations. PhD thesis The Open University.



The intentionof this thesis is to examine the role of the neocortical local drcuit in supporting synchronisatLon and fast (gamma) oscUlation. The aim is to include stereotypical features of the local neocortex in model simulations of cortical activity. Modelling is hmitedby scale in number and detail. Model features include three neurontypes(RS, FS and IB) andsynapses with three time courses takenfrom reportedtri-phasic PSPs (fEPSP, flPSP andsIPSP). Cell types and synapses are distributedin a two layer model.

The contribution of the layers to columnactivity is investigated. The upperlayer has a tendancy towardspredse synchronisation and can dominate the activity producing synchronisation and oscillation in the whole column. This is attributed to the stronger inhibitory circuit in the upperlayer. The lower layer achieves a less precise synchronisatiorv this is attributed to a lower level of inhibition and the intraburst duration of IB neurons.

The significance of this difference in the temporal properties of the two layers is discussed in relation to existing theories andmodels of local cortical function. Following a further consideration of local cortical physiology a new model of cortical functioning is proposed. The key features of this model include: the generation of local oscillations in a vertical interlarninar reciprocal circuit; the apical dendrite providing a sharp coincidence detection functionbetweenthe layers; slow axonal lateral propagationprovidinga time delay network; apical dendrites of bursting cells (CH and IB) providing coincidence detectionbetweenmputs 6:0m distant areas (layer 1 inputs) and local activity; bursting cell innervationof intemeurons, linking the local oscillation cy de to coinddence detection. This moddis termed an'intrinsically osdllating time coding networld (lOTCN). Specific predictions are made concerning the functiorungof the local circuit m neocortex, and the connectivity of CH neurons.

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