Cell density impacts population activity in human iPSC-derived neural networks.

Multi-electrode recording of neuronal activity in cultures offer opportunities for understanding how the structure of a network gives rise to function. Neuronal cultures derived from human induced pluripotent stem cells (iPSCs) from male and female individuals are often plated at highly variable cell densities across studies, but its impact on neuronal activity remains poorly understood. We found that properties such as the mean firing rate of the individual cells, the pair-wise correlations between cells, and the entropy of the population all changed significantly with changes in culture density. We used a maximum entropy model to capture the structure of the population activity using only the firing rates and correlations, we found that the model performed best at the highest densities, suggesting that changes in activity reflected differences in structure of interactions between neurons across scales of complexity. Our work thus shows that culture density is an important experimental parameter that impacts neuronal activity in human iPSC-derived cultures. Additionally, our findings provide an analytical framework to study population activity in neuronal cultures including those from patient populations where a disease process may impact network activity.Significance statement iPSC-derived human neuronal cultures have been used to study the emergent patterns of population activity across development and in disease models. Across these studies, the culture density is one of the most variable experimental parameters, but it is unclear to what extent density affects population activity. By performing multi-electrode array (MEA) recordings of neuronal cultures at different densities, we identified how increasing the cellular density decreased the complexity of patterns of population activity.