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Abstract

The balance of excitation and inhibition in neuronal circuits is essential for stable dynamics. This is probably why various brain regions show distinct and highly conserved ratios of excitatory and inhibitory neurons. However, it is unclear if biological neuronal networks with artificial ratios of inhibitory and excitatory neurons would exhibit changes in dynamics. Moreover, it is unclear whether the artificial ratios would jeopardize the balance of excitation and inhibition on a synaptic level. To investigate these questions, we recorded the Ca-activity of hippocampal cultures with various fractions of inhibitory neurons. All cultures developed spontaneous network bursting. The cultures with various fractions of inhibitory neurons showed stable mean inter-burst intervals. However, the variance of inter-burst intervals grew with the number of inhibitory neurons. We reproduced the results of experiments in a model network of adaptive leaky integrate-and-fire neurons with different numbers of inhibitory neurons but the balanced numbers of excitatory and inhibitory synapses. Overall, our results suggest that hippocampal cultures with various cellular compositions tend to maintain the balance of excitation and inhibition.