Influence of synchronous and asynchronous signals from pyramidal neurons on synchronization of GABAergic interneuronal networks on the hippocampus

We investigated the impact of the level of stochastic excitation of synaptic signals from pyramidal neurons on the generation of oscillations inside the interneuronal networks of the hippocampus with shunting GABAergic synapses. We used a modification of a mathematical model of the interneuronal networks (I. Vida, M. Bartos and P. Jonas, 2006) together with a model of external synaptic signalling with a Poisson distribution of time interval between events. We demonstrated that a completely synchronized synaptic signal when every interneuron in the network was impacted by an electric current with the same amplitude and frequency caused oscillations with a high level of synchronization (k > 0,9) in the network. The increase of synaptic signal frequency led to the respective increasing of oscillation frequency in the network. We demonstrated that a gradual increase of stochastic synaptic current from 0.001 to 0.200 causes reduction of synchronisation of oscillations in the interneuronal network from 0.89 to 0.11 with an equal signal frequency of 6 Hz. The frequency of oscillations in the interneuronal network also decreased from 55.6 to 35.7 Hz respectively for the levels of stochastisity 0.001 to 0.200 and the frequency of excitation of 58 Hz. Decrease of frequency and synchronization of oscillations in the network could be explained by the the inability of shunting GABAergic synapses to synchronize the work of separate interneurons when there is significant increase in stochastic external excitation. Besides this, we demonstrated the existence of a range of frequencies of the incoming signal of 30–40 Hz in the network, of which a significant increase of synchronisation of oscillations in the network takes place regardless of the stages of external stochastic excitation.