Cooperation and competition of gamma oscillation mechanisms.

Oscillations of neuronal activity in different frequency ranges are thought to reflect important aspects of cortical network dynamics. Here, we investigate how various mechanisms that contribute to oscillations in neuronal networks may interact. We focus on networks with inhibitory, excitatory and electrical synapses, where the subnetwork of inhibitory interneurons alone can generate interneuron gamma oscillations (ING) and the interactions between interneurons and pyramidal cells allow for pyramidal-interneuron gamma oscillations (PING). What type of oscillation will such a network generate? We find that ING and PING oscillations compete: The mechanism generating the higher oscillation frequency "wins", it determines the frequency of the network oscillation and suppresses the other mechanism. For type-I interneurons, the network oscillation frequency is equal to or slightly above the higher of the ING and PING frequencies in corresponding reduced networks that can generate only either of them. If the interneurons belong to the type-II class, it is in between. In contrast to ING and PING, oscillations mediated by gap junctions and oscillations mediated by inhibitory synapses may cooperate or compete, depending on the type (I or II) of interneurons and the strengths of the electrical and chemical synapses. We support our computer simulations by a theoretical model that allows a full theoretical analysis of the main results. Our study suggests experimental approaches to decide to what extent oscillatory activity in networks of interacting excitatory and inhibitory neurons are dominated by ING or PING oscillations and of which class the participating interneurons are.

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