The analysis of dynamics and the relationship between spontaneous and evoked activity as cell assemblies in a...

In a brain, it is considered that the synchronous activity of neurons expresses a representation of information. Hebb named the synchronous active group of neurons "Cell Assembly". In this study, we hypothesized that a repeatedly expressed pattern is a cell assembly representing a certain kind of information and attempted to extract such "Cell Assembly" by X-means clustering based on spatiotemporal continuity of spontaneous spikes. Moreover, we divided cell assemblies into classes consist of similar types of cell assemblies, using the indiscernibility-based clustering, "rough clustering". As the result, it showed that cell assemblies did not have a large temporal extent, but a spatial extent. Additionally, we analyzed the neuronal network activity as the stochastic process whose state space is the set of cell assembly, finding out that similar patterns appear consecutively. According to these results, information processing in the neuronal network is suggested to be the hierarchical process. Finally, the clustering method was adopted for spontaneous activity and the evoked responses. It is suggested that spontaneous activities and evoked responses are not completely independent, but share resemble activities.