Balance between inhibitory cell types is necessary for flexible frequency switching in adult mouse visual cortex

Abstract

Neuronal networks in rodent primary visual cortex (V1) can generate oscillations in different frequency bands depending on the network state and the level of visual stimulation. High-frequency gamma rhythms, for example, dominate the networks spontaneous activity in adult mice but are attenuated upon visual stimulation, during which the network switches to the beta band instead. The spontaneous LFP of juvenile mouse V1, however, mainly contains beta oscillations and presenting a stimulus does not elicit drastic changes in collective network oscillations. We study, in a spiking neuron network model, the mechanism in adult mice that allows for flexible switches between multiple frequency bands and contrast this to the network structure in juvenile mice that do not posses this flexibility. The model is comprised of excitatory pyramidal cells (PCs) and two types of inhibitory interneurons: the parvalbumin expressing (PV) interneuron, which produces gamma oscillations, and the somatostatin expressing (SOM) cell, which generates beta rhythms. Our model simulations suggest that both of these oscillations are generated by a pyramidal-interneuron gamma (PING) mechanism. Furthermore, prominent gamma and beta oscillations in, respectively, the spontaneous and visually evoked activity of the simulated network only occurred within the same network configuration when there was a balance between both types of interneurons so that SOM neurons are able to shape the dynamics of the pyramidal-PV cell subnetwork without dominating dynamics. Taken together, our results demonstrate that the effective strengths of PV and SOM cells must be balanced for experimentally observed V1 dynamics in adult mice. Moreover, since spontaneous gamma rhythms emerge during the well-known critical period, our findings support the notion that PV cells become integrated in the circuit of this cortical area during this time window and additionally indicate that this integration comprises an overall increase in their synaptic strength.