Cover picture: An example of a two-dimensional cross-correlogram. This matrix shows the variation in time of the strength of correlated activity of two neurons. The diagonal of the matrix represents the correlation strength at zero time lag. The points above and below this diagonal represent positive and negative time delays between the two neurons. Neurons in the primary visual cortex start to synchronize their activity (red part of the diagonal) before the onset of the stimulus in a figure-ground detection task. Such a switch in the internal state of the primary visual cortex is necessary for the detection of the stimulus. For details, see the article by Supèr et al. in this issue (pages 3407–3414).