Mesoscale Architecture Shapes Initiation and Richness of Spontaneous Network Activity

Abstract

Spontaneous activity in the absence of external input, including propagating waves of activity, is a robust feature of neuronal networks and The neurophysiological and anatomical requirements for initiation and persistence of such activity, however, are poorly understood, as is their role in the function of neuronal networks. Computational network studies indicate that clustered connectivity may foster the generation, maintenance, and richness of spontaneous activity. Since this mesoscale architecture cannot be systematically modified in intact tissue, testing these predictions is impracticable Here, we investigate how the mesoscale structure shapes spontaneous activity in generic networks of rat cortical neurons In these networks, neurons spontaneously arrange into local clusters with high neurite density and form fasciculating long-range axons. We modified this structure by modulation of protein kinase C, an enzyme regulating neurite growth and cell migration. Inhibition of protein kinase C reduced neuronal aggregation and fasciculation of axons, i.e., promoted uniform architecture. Conversely, activation of protein kinase C promoted aggregation of neurons into clusters, local connectivity, and bundling of long-range axons. Supporting predictions from theory, clustered networks were more spontaneously active and generated diverse activity patterns. Neurons within clusters received stronger synaptic inputs and displayed increased membrane potential fluctuations. Intensified clustering promoted the initiation of synchronous bursting events but entailed incomplete network recruitment. Moderately clustered networks appear optimal for initiation and propagation of diverse patterns of activity. Our findings support a crucial role of the mesoscale architectures in the regulation of spontaneous activity dynamics. Computational studies predict richer and persisting spatiotemporal patterns of spontaneous activity in neuronal networks with neuron clustering. To test this, we created networks of varying architecture Supporting these predictions, the generation and spatiotemporal patterns of propagation were most variable in networks with intermediate clustering and lowest in uniform networks. Grid-like clustering, on the other hand, facilitated spontaneous activity but led to degenerating patterns of propagation. Neurons outside clusters had weaker synaptic input than neurons within clusters, in which increased membrane potential fluctuations facilitated the initiation of synchronized spike activity. Our results thus show that the intermediate level organization of neuronal networks strongly influences the dynamics of their activity.

Dominance of Metric Correlations in Two-Dimensional Neuronal Cultures Described through a Random Field Ising Model

“…We conjecture that metric effects overshadow the distribution of connections to such an extreme that they mold the dynamic attributes of the network. Such an idea is supported by experimental results in neuronal cultures [10,32]. For instance, the analysis of activity fronts in homogeneous cultures similar to ours (δ ≃ 0.1, Λ ≃ 0.2) revealed that metric correlations provide amplification mechanisms for the fronts to spontaneously emerge [10].…”

Landau–Ginzburg theory of cortex dynamics: Scale-free avalanches emerge at the edge of synchronization

“…heterogeneous in space, is able to reproduce remarkably well empirical in vitro results for neural cultures with different levels of mesoscopic structural heterogeneity (79).…”

Development of network structure and synchronized firing patterns in dissociated culture of neurons

“…For example, Okujeni et al. reported that appropriately clustered networks underlie diverse synchronized firing patterns in vitro . There is also a possibility that “rich‐club” network structures support generation of synchronized firing patterns .…”