When an oscilloscope's audio monitor starts to screech rhythmically in a neurophysiology lab, its waves hint at one of the most puzzling patterns in biology. Sometimes multiple neurons will simply fire synchronously, multiplying the strength of a signal. But what has intrigued researchers since the 1920s, when Hans Berger first started describing EEG patterns, is that often these synchronous neurons produce oscillatory rhythms, detectable as waves of distinct frequencies. "Synchronous oscillations are conserved among widely different species, which suggests that they are important in neural processing," says Ole Paulsen of Oxford University, who will be chairing a symposium on Network Oscillations at this month's Society for Neuroscience meeting. "What role they play, we still do not know."