Figure 5. Network architecture and NMDAR recruitment at feedback connections.

(A) Schematic of network structure. (B) Voltage traces of interneuron (black) and principal cells (blue, cell # at right) during network simulation. The network was driven by an asynchronous barrage of spikes, maximal in cell #125 (‘clustered’ input). (C) Corresponding currents in interneuron. Red: NMDAR currents from principal cells; green: GABAR currents from autaptic PV+ cell connections; black: sum of NMDAR and AMPAR currents from principal cells; gray: AMPAR currents from external drive. (D) Left: schematic showing cell assemblies receiving clustered (top) or dispersed (bottom) external inputs, and middle: corresponding summary plots of network simulation showing external drive input distribution (gray), pyramidal cell firing (blue, circles), and interneuron firing (black, and vertical dashed lines). Right: average NMDAR and AMPAR charge in interneuron per principal neuron spike. (Autaptic and feedback connections from PV+ cells are omitted from the schematic for clarity.).

Figure 5—figure supplement 1. Modeling principal cell input cooperation onto feedback interneurons.

(A) Network schematic showing postsynaptic membrane locations of Izhikevich-model PV+ interneuron. (B) Steady state transfer resistance for a PV+ cell dendritic tree reconstructed using the TREES toolbox (Cuntz et al., 2010). The matrix shows the electrotonic ‘proximity’ of neighbouring patches of membrane on the dendritic tree (color scale: µV/pA). The main branches of the dendritic tree are indicated at the bottom. (C) Input cooperativity matrix used in simulations. Inset shows zoomed view of cooperativity matrix for the first 50 principal neurons.

Figure 5—figure supplement 2. NMDARs help to maintain a sparse and sharp representation of a ‘hump’ of excitation to the feedback circuit shown in Figure 5D.

(A) Distribution of firing rate by neuron during each PV+ interneuron firing cycle, averaged across 500 simulations. Top – without NMDARs, bottom – with NMDARs. The hump of excitation was centered on neuron #125. Note the similarity of the first cycle between the two conditions. The behaviors of the networks diverge as the NMDARs are engaged. (B) As (A) but normalized by total firing rates across neurons, for better comparison of distribution dispersion. (C) Comparison of first and tenth simulation cycle: top – mean spikes per cycle, bottom - standard deviation of average network ‘receptive field’.