Reorganization of Burst Initiation Zones as a Signature of Stimulation-Induced Plasticity in In Vitro Cortical Networks.

The spontaneous activity of neuronal cultures is dominated by periods of coherent activity known as network bursts The dynamics of the initiation and propagation of these bursts are believed to depend on the structural connectivity of the neuronal network. Specifically, the spatial loci of burst initiation, referred to as initiation zones (IZs), are shaped by a complex interplay between dynamics and connectivity, with the particular structure of the latter playing a crucial role. Thus, alterations in network structure, such as those following from plasticity mechanisms activated by perturbations, are expected to lead to changes in network burst dynamics. To shed light on this point, we investigated the effect of localized electrical stimulation on the initiation of network bursts in in vitro cortical networks from embryonic rats of either sex cultured on high-density microelectrode arrays, and observed that electrical stimulation significantly altered the spatial patterning of IZs. To explore the mechanisms underlying these alterations, we assessed changes in effective connectivity (EC) using transfer entropy. Although both IZs and EC exhibited similar remodeling following stimulation, EC alone could not fully account for the observed IZ shifts. Moreover, IZ remodeling was largely unpredictable and independent of the stimulation site, suggesting that the observed changes were due to large-scale remodeling of connectivity structure, likely involving local potentiation/depotentiation and homeostatic mechanisms. Our findings provide evidence that electrical stimulation can remodel burst initiation and effective connectivity, although achieving precise local control appears unattainable.