We present an overview of the investigations on Synchronized Spontaneous Activity (SSA) in the somatosensory and visual modality. The novelty of the stimulation paradigm and of the off-line data analysis, as well as the capability of the neuromagnetic technique to localize and follow in time the generators responsible for the SSA are used to characterize SSA and to study the underlying spontaneous activity. Synchronization of alpha and mu rhythms have been recognized and studied. The possibilities opened by the technique are discussed.