Abstract The recent upraise of interest in the dynamics of the brain resting activity opens a number of new and different questions. A fundamental one is related to the character of correlations of healthy large scale brain activity. These studies focus on the linear correlation of the spontaneous activity between brain sites. Here we present a different approach, instead to estimate the average linear correlation of activity between pairs of brain sites, we ask: what are average sequels in space and time of a big event (i.e., a thunder). By strobing these events we find that on average the activity variations with opposite sign are correlated in time, over a temporal scale of few seconds, exposing a critical balance between excitation and depression opposing forces.