he rhythmic activity of neurons in the brain has fascinated neuroscientists ever since electrical potentials were first recorded from the human scalp more than 70 years ago. The rhythms of electrical activity in sensory neurons that encode visual information are known to vary markedly with attention. How does neuronal encoding differ for a visual stimulus that is the center of attention compared with one that is ignored? To answer this question, Fries et al. (1) simultaneously recorded electrical activity from several clusters of neurons in the V4 region of the visual cortex of macaque monkeys that were shown behaviorally relevant and distracter objects (see the figure). On page 1560 of this issue, they report a rapid increase in the synchronization of electrical activity in the gamma frequency range (35 to 90 Hz) in V4 neurons activated by the attended stimulus (that is, the stimulus on which attention is focused) but not in V4 neurons activated by distracter objects (1).