||Synchronization is investigated in the two-dimensional clusterized cortical neuronal network in vitro. The firing activity of the network is stained by fluorescence calcium indicator under the depletion of magnesium ions and monitored by the confocal microscopy with 10 Hz EMCCD. At high density (» 9000 cells/mm2), neurons self-organize into the two-dimensional clusterized neuronal network interconnected by three-dimensional clusters. Due to the spatial heterogeneity of the clusterized network at high density, the cortical neuronal network has rich spatiotemporal firing dynamics. It has been identified that the envelopes of bursting neurons within clusters are synchronous. At inter-cluster level, the firing delay between clusters is investigated at fine temporal scale. The firing order between these clusters exists on 8th day in vitro (DIV). Through tuning the mutual coupling strength and stochastic noise in the environment, it is found that not only the firing delay is enhanced, but also the firing order between clusters is exchanged. As day goes by, the firing burst rate increases, because the stronger coupling strength between clusters enhance. In the presence of the spatial heterogeneous neuronal network, the slower time scale dynamics, the burst of action potential burst, is explored on 14th»17th DIV. Standing on the nonlinear dynamics, several mechanisms are proposed and verified. This phenomenon still calls for more biological assays to verify.|
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