Network Dynamics and Spontaneous Oscillations in a Developing Neuronal Culture

Biological neuronal networks are highly complex and studying such networks is important to understand its functionality. Neuronal networks are dynamic especially during the developmental stages of the brain where new neurons and synapses form and will continue through the lifespan of an organism. Developing networks in in vitro often self-organize into functional networks that produce spontaneously synchronizing oscillations even in the absence of external stimuli. The nature of network dynamics and its relationship to spontaneous oscillations and synchrony is not well-known. In this study this relationship is investigated. Neurons from newborn rat cortices were extracted and cultured over transparent microelectrode arrays. Neurons and neurite extensions were traced by imaging the culture at different stages of development. The anatomical connectivity was mathematically abstracted as a simple undirected graph. Simultaneously, multisite basal activities were recorded using microelectrodes and analyzed for the degree of synchrony. The networks were found to be neither random nor completely organized, but rather semi-random (also known as small-world networks). Spontaneous oscillations were observed once neurons began to form local connections. The network exhibited global synchronous oscillations when small-world network properties began to emerge. Our results indicate that the ability of networks to self-organize into a small-world network correlates with origin of sustained synchronous activity.