Temporal organization of ongoing brain activity

Ongoing brain activity results from the mutual interaction of hundred billions non-linear units and represents a significant part of the overall brain activity. Although its complex dynamics has been widely investigated, a large number of fundamental questions are still open,many of them concerning its temporal structure. Why does a certain population of neurons fires synchronously? Are these synchronized bursts following each other randomly or are they correlated according to some organizing principle? Far from addressing the fundamental problem of its functions, in the present article we focus on the problem of temporal correlations of ongoing cortical activity. We first overview the major features of its temporal structure and review recent experimental results, with particular emphasis on alternative approaches inspired in the theory of stochastic processes; then we introduce a neuronal network model inspired in self organized criticality and compare numerical results with experimental findings.