Slow oscillating population activity in developing cortical networks: models and experimental results

During early development neuronal networks express slow oscillating synchronized activity. The activity can be driven by several, not necessarily mutually exclusive, mechanisms. Each mechanism might have distinctive consequences for the phenomenology, formation, or sustainment of the early activity pattern. Here we study the emergence of the oscillatory activity in three computational models and multisite extracellular recordings that we obtained from developing cortical networks in vitro. The modeled networks consist of leaky integrate-and-fire neurons with adaptation coupled via depressing synapses, which were driven by neurons that are intrinsically bursting, intrinsically random spiking, or driven by spontaneous synaptic activity. The activity of model networks driven by intrinsically bursting cells best matched the phenomenology of 1-wk-old cultures, in which early oscillatory activity has just begun. Intrinsically bursting neurons were present in cortical cultures, but we found them only in those cultures that were younger than 3 wk in vitro. On the other hand, synaptically dependent random spiking was highest after 3 wk in vitro. In conclusion, model networks driven by intrinsically bursting cells show a good approximation of the emergent recurrent population activity in young networks, whereas the activity of more mature networks seems to be better explained by spontaneous synaptic activity. Moreover, similar to previous experimental observations, distributed stimulation in the model was more effective in suppressing population bursts than repeated stimulation of the same neurons. This observation can be explained by an effective depression of a larger fraction of synapses by distributed stimulation.