Estimation of Thalamocortical and Intracortical Network Models fromJoint Thalamic Single-Electrode and Cortical Laminar-Electrode Recordings in theRat Barrel System

摘要

A new method is presented for extraction of population firing-rate models for both thalamocortical and intracortical signal transfer based on stimulus-evoked data from simultaneous thalamic single-electrode and cortical recordings using linear (laminar) multielectrodes in the rat barrel system. Time-dependent population firing rates for granular (layer 4), supragranular (layer 2/3), and infragranular (layer 5) populations in a barrel column and the thalamic population in the homologous barreloid are extracted from the high-frequency portion (multi-unit activity; MUA) of the recorded extracellular signals. These extracted firing rates are in turn used to identify population firing-rate models formulated as integral equations with exponentially decaying coupling kernels, allowing for straightforward transformation to the more common firing-rate formulation in terms of differential equations. Optimal model structures and model parameters are identified by minimizing the deviation between model firing rates and the experimentally extracted population firing rates. For the thalamocortical transfer, the experimental data favor a model with fast feedforward excitation from thalamus to the layer-4 laminar population combined with a slower inhibitory process due to feedforward and/or recurrentconnections and mixed linear-parabolic activation functions. The extractedfiring rates of the various cortical laminar populations are found to exhibitstrong temporal correlations for the present experimental paradigm, and simplefeedforward population firing-rate models combined with linear or mixedlinear-parabolic activation function are found to provide excellent fits to thedata. The identified thalamocortical and intracortical network models are thusfound to be qualitatively very different. While the thalamocortical circuit isoptimally stimulated by rapid changes in the thalamic firing rate, theintracortical circuits are low-pass and respond most strongly to slowly varyinginputs from the cortical layer-4 population.